// Program  to display inches and millimeters by accepting centimeters

#include<stdio.h>

void main()
{
 float cm,inches,mm;

  printf("Enter number of centimeters :");
  scanf("%f",&cm);

  inches = cm / 2.5;
  mm = cm * 10;

  //  %.2f is to display only two decimal places
  printf("For %.2f Centimeter, Inches are %.2f and Millimeters are %.2f \n",cm,inches,mm);

}

Accept price and quantity and display amount

// Program to take quantity and price and display amount

#include<stdio.h>

void main()
{
   float price,qty,amount;


    printf("Enter price    :");
    scanf("%f",&price);

    printf("Enter quantity :");
    scanf("%f",&qty);

    amount=price * qty;

    printf("Amount =  %f \n",amount);

}

Accept a number and display cube of the given number

// Cube for given number

#include<stdio.h>

void main()
{
   int num,cube;

    printf("Enter a number :");
    scanf("%d",&num);

    cube=num * num * num;

    printf("Cube  for %d  is %d \n",num, cube);

}

Lesson 2 - Language Elements

Accept basic salary and calculate net salary by adding 40% HRA, 20% DA, and subtracting 5% PF

// Program to calculate net salary

#include<stdio.h>

void main()
{
    float salary,hra,da,pf,netsalary;

     printf("Enter salary :");
     scanf("%f",&salary);

     hra = salary * 0.4;
     da  = salary * 0.2;
     pf = salary * 0.05;

     netsalary=salary + hra + da - pf;

     // Display net salary without any decimal portion
     printf("Net salary = %.0f\n",netsalary);
}

Accept two numbers and interchange them with and without using third variable.

// Program to interchange values of two variables without using 3rd variable

#include<stdio.h>

void main()
{
 int a,b, temp;

  printf("Enter two numbers :");
  scanf("%d%d",&a,&b);

  // By using third variable 
  temp = a;
  a = b;
  b = temp;

  printf("value of a = %d and value of b = %d \n",a,b);

  // Without using thrid variable
  a = a + b;
  b = a - b;
  a = a - b;

  printf("value of a = %d and value of b = %d \n",a,b);
}

Lesson 4 - Control Statements

Accept month number and year and display exact number of days in the given month.

// Program to display number of days in the given month and year

#include<stdio.h>

main()
{
    int month,year, nodays;

      printf("Enter Month [1-12] :");
      scanf("%d",&month);
      printf("Enter 4 digit year :");
      scanf("%d",&year);

      switch(month)
      {
       case 2 :
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
                    nodays = 29;
            else
                    nodays = 28;
            break;
       case 4:
       case 6:
       case 9:
       case 11:
            nodays = 30;
            break;
       default:
            nodays = 31;
      }

      printf("We have %d days in month %d of year %d\n", nodays,month,year);
}

Accept quantity and price from user and display net amount to be paid. Apply 20 % discount if quantity is more than 5 or 10% if quantity is more than 2. Apply additional 10% discount if total amount crosses 1000.

// Program to calculate net amount

#include<stdio.h>

main()
{
    float qty, price, amount;

      printf("Enter Price    :");
      scanf("%f",&price);
      printf("Enter Quantity :");
      scanf("%f",&qty);

      amount = qty * price;

      if (qty > 5)
          amount = amount * 0.80;    // 20% discount
      else
          if (qty > 2)
            amount = amount * 0.90;  // 10% discount


      // calculate additional discount
      if ( amount > 1000)
           amount *= 0.90;

      printf("Net Amount     :%.2f\n",amount);  // display amount with decimal places
}

Accept marks from user and display grade based on the following table :

Marks	Grade
>80	A
>70	B
>60	C
<=60	D

// Program to print grade based on marks 

#include<stdio.h>

main()
{
    int marks;

      printf("Enter Marks :");
      scanf("%d",&marks);

      if (marks > 80)
          printf("A");
      else
        if (marks > 70)
          printf("B");
        else
         if (marks > 60)
           printf("C");
         else
            printf("D");

}

Accept three numbers and display the biggest of three numbers.

// Program to find out biggest of three numbers

#include<stdio.h>
main()
{
    int a,b,c,big;

      printf("Enter three  numbers :");
      scanf("%d%d%d",&a,&b,&c);  // enter three numbers with space separating them

      if(a>b)
      {
          if(a>c)
              big = a;
          else
              big = c;
      }
      else
      {
         if(b>c)
             big = b;
         else
             big = c;
      }

      printf("Biggest number is %d\n", big);
}

Accept marks in two subjects and display grade as follows:

Fail if marks in any subject are less than 50
Grade A if marks in each subject are more than 80
Grade B if marks in any one subject are more than 80
Grade C if total marks are more than 150
Otherwise Grade D

// Program to calculate grades based on given marks

#include<stdio.h>

void main()
{
  int  marks1, marks2;

    printf("Enter marks for two subjects :");
    scanf("%d%d",&marks1, &marks2);


    if ( marks1 < 50 || marks2 < 50)
         printf("Failed\n");
    else
      if( marks1 > 80 && marks2 > 80 )
          printf("Grade A \n");
      else
        if ( marks1 > 80 || marks2 > 80)
              printf("Grade B \n");
        else
            if ( marks1 + marks2 > 150)
                printf("Grade C \n");
            else
                printf("Grade D \n");

}

Lesson 6 - Looping Structures

Accept 10 numbers and display the biggest number

// Program to display biggest of 10 numbers
        
#include<stdio.h>

void main()
{
   int i=1,num,big;


    big=0;
    for(i=1; i <= 10; i ++)
    {
       printf("Enter a number :");
       scanf("%d",&num);
       if(num > big)
           big = num;
    }

    printf("\nBiggest = %d \n",big);
}

Accept a number and display whether it is a prime number

// Program to display prime number or not

#include<stdio.h>

main()
{
  int n,i,prime = 1;

  printf("Enter a number :");
  scanf("%d",&n);

  for(i=2; i <= n/2; i++)
  {
      if(n % i == 0)
      {
        prime = 0;  // false
        break;
      }
  }

  if(prime)  // if prime is non-zero
      printf("%d is prime number\n",n);
  else
      printf("%d is not a prime number!\n",n);

}

Accept base and power and display the result

// Program to accept base and power and display the result  (base raised to power)

#include <stdio.h>

void main( )
{
    int base,power, result=1 , i;


        printf("Enter Base  :");
        scanf("%d",&base);
        printf("Enter Power :");
        scanf("%d",&power);

        for(i=1;i<=power;i++)
        {
            result *= base;
        }

        printf("%d raised to %d = %d\n", base,power,result);

}

Display table for number 9 from 10 to 20

           Sample Output : 
           9 * 10 = 90
           9 * 11 = 99
           …
           9 * 20 = 180

// Program to display table for 9 from 10 to 20

#include<stdio.h>

void main()
{
    int r,i;

     for(i=10; i<=20 ;i++)
     {
        printf("%2d * %2d = %4d\n", 9, i, 9 * i);
     }
}

Display first 10 numbers in Fibonacci series

//  First 10 numbers in fibonacci series

#include<stdio.h>

void main()
{
    int prev=0,current=1,next, i;


     printf("%d\n%d\n", prev,current);
     for(i=3; i <= 10; i ++)
     {
        next = prev + current;
        prev = current;
        current = next;
        printf("%d\n",next);
     }
}

Accept two numbers and display GCD (Greatest Common Divisor)

// Program to display GCD of 2 numbers

#include<stdio.h>

void main()
{
    int a,b,small,i;

     printf("Enter Two Numbers : ");
     scanf("%d %d",&a,&b);

     small = a < b ? a : b;  // start with smallest of two numbers

     for(i=small; i>=1; i --)
     {
         if( a % i == 0 && b % i == 0)
              break;
     }

     printf("GCD of %d and %d is %d\n", a, b, i);
}

Print sum of digits for numbers between 1000 and 9999

// Sum of digits for numbers between 1000 and 9999 */

#include <stdio.h>

void main()
{
    int n,i,r,sum;

     for(i=1000; i <= 9999; i++)
     {
        n=i;
        sum=0;
        while(n!=0)
        {
            r= n % 10;
            sum += r;
            n = n / 10;
        }
        printf("%d  %d\n",i,sum);
     }
}

Lesson 8 - Arrays

Take an array of 10 elements, fill it with random numbers and then reverse array without using any second array.

// Program to fill array with random numbers and reveres array without using another array

#include<stdio.h>

void main()
{
   int a[10];
   int n,i,j,temp;

   srand(time(0));
   printf("\nOriginal Array\n");
   for(i=0;i<10;i++)
   {
     a[i]=rand()%100;
     printf("%d\t", a[i]);
   }

   // reverse array
   for(i=9,j=0;j < i ;i--,j++)
   {
       temp=a[j];
       a[j]=a[i];
       a[i]=temp;
   }

   printf("\nArray after reversing it\n");

   for(i=0;i<10;i++)
     printf("%d\t",a[i]);
}

Delete the element at the given position from an array of 10 elements and fill the last element with 0.

// Program to delete the element at the given position from an array of 10 elements and fill the last element with 0

#include<stdio.h>

void main()
{
    int a[10],i,pos;

    srand(time(0)); // Initialize seed
    // Fill array with random numbers
    for(i=0;i<10;i++)
    {
      a[i] = rand() % 100;
      printf("%d\t", a[i]);
    }

    printf("\nEnter position of element to delete :");
    scanf("%d",&pos);

    for(i=pos;i < 9; i++)
    {
      a[i]=a[i+1];
    }

    a[9]=0; // Set last element to 0

    printf("\nArray after deletion\n");
    for(i=0;i<10;i++)
      printf("%2d\t",a[i]);
}

Read numbers from keyboard and copy them into an array of 5 elements. Make sure only positive numbers are copied into array and negative numbers are ignored.

// Program to read numbers from keyboard and place only positive numbers into array

#include<stdio.h>

main()
{
  int i=0,count=0,n;
  int a[5];

   while(i<5)
   {
    printf("Enter a number : ");
    scanf("%d",&n);
    if(n > 0)
    {
      a[i]=n;
      i++;
    }
   }

   for(i=0;i<5;i++)
     printf("%d\n",a[i]);
}

Print all even numbers of an array of 10 elements first and then odd numbers.

//Program to print even numbers first then odd numbers of an Array

#include<stdio.h>

void main()
{
  int i,j=0,n;
  int a[10];

   srand(time(0));
   // Fill array with random numbers
   for(i=0;i < 10;i++)
    a[i] = rand() % 100;

   // Print even numbers
   printf("\nEven Numbers\n");
   for(i=0;i<10;i++)
   {
     if( a[i] % 2 == 0)
        printf("%d\n",a[i]);
   }

   // Print odd numbers
   printf("\nOdd Numbers\n");
   for(i=0;i<10;i++)
   {
     if( a[i] % 2 != 0)
        printf("%d\n",a[i]);
   }
}

Lesson 10 - Chars and Strings

Accept a string and count number of words

// Program to count number of words in string

#include<stdio.h>
#include<string.h>

main()
{
  int count=0,i,inword;
  char st[50];

    printf("Enter a string :");
    gets(st);

    inword = 0;
    for(i=0; st[i] != '\0'; i++)
    {
        if(st[i] == 32)
           inword = 0;  // not in word
        else
            if(!inword) // if not in word then increment count
            {
                inword = 1;
                count++;
           }
    }
    printf("Word count =  %d\n",count);
}

Accept 10 characters without echoing and print their inverse case

// Program to accept 10 characters without echoing and print their inverse case

#include<stdio.h>
#include<ctype.h>

main()
{
  int i;
  char ch;

  printf("Enter 10 characters\n");

  for(i=0;i<10;i++)
  {
      ch = getch();
      if (isupper(ch))
       putch(tolower(ch));
      else
       putch(toupper(ch));
  }
}

Accept password (without echoing characters) and check whether it has a digit, alphabet and special character – or @

// Program to accept password (without echoing characters) and check whether it has a digit, alphabet and special character – or @

#include<stdio.h>
#include<string.h>

main()
{
    int i,alpha=0,digit=0,special=0;
    char pwd;

    printf("Enter password [enter to stop] :");

    do
    {
        pwd = getch();  // take one char without echo
        if(isalpha(pwd))
          alpha++;
        else
          if(isdigit(pwd))
            digit++;
          else
             if(pwd =='-' || pwd == '@')
                special++;

    }
    while(pwd!=10);  // until new line is entered

    if(alpha > 0 &&  digit > 0 && special > 0 )
      printf("\nPassword is valid!\n");
    else
      printf("\nPassword is invalid!\n");

}

Accept 10 strings and print the largest string

// Accept 10 strings and print the largest string

#include<stdio.h>
#include<string.h>

main()
{
   int i;
   char st[20], largest[20];

    // initialize largest to empty string
    largest[0]= '\0';
    for(i=0;i<10;i++)
    {
        printf("Enter a string : ");
        gets(st);

        if(strcmp(st,largest) > 0 )
           strcpy(largest,st);
    }

    printf("Largest String = %s\n",largest);

}

Print each word in a string in reverse order

// Program to print each word in a string in reverse order

#include<stdio.h>
#include<string.h>

void main()
{
   int i,j;
   char st[100],word[20];

    printf("Enter a string :");
    gets(st);

    for(i=0, j=0; ;i++)
    {
        if(st[i] == 32 || st[i] == '\0') // print
        {
           if ( j > 0) // if word has any char
           {
            for(--j; j >=0; j --)
            {
                putch(word[j]);
            }
            printf("\n");
            j = 0;
           }
           if(st[i] == '\0') // stop if end of string reached
              break;
        }
        else
            word[j++] = st[i];
    }
}

Accept two strings and check whether they have same set of characters

// Program to check whether two strings have same set of chars 

#include <stdio.h>

main()
{
  char st1[50], st2[50];
  int i,j, found;


  printf("Enter first string  : ");
  gets(st1);

  printf("Enter second string : ");
  gets(st2);

  // Check whether every char in first string is present in second string
  for(i=0; st1[i] ; i ++)
  {
      found = 0;
      for(j = 0; st2[j]; j ++)
      {
          if (st1[i] == st2[j])
          {
            found = 1;
            break;
          }
      }

      if (!found) {
        printf("Strings do not have same set of chars");
        exit(0); // terminate program
      }
  }

  // Check whether every char in second string is present in first string
  for(i = 0; st2[i] ; i ++)
  {
      found = 0;
      for(j = 0; st1[j]; j ++)
      {
          if (st2[i] == st1[j])
          {
            found = 1;
            break;
          }
      }

      if (!found) {
        printf("Strings do not have same set of chars");
        exit(0); // terminate program
      }
  }

  printf("\nBoth strings have same set of chars\n");

}

Lesson 12- User-defined Functions

Create a function that takes a number and returns 1 if number is prime, otherwise 0.

// Create a function to check whether a number is prime

#include<stdio.h>
int prime(int num);

main ()
{
  int n,a;

   printf("Enter a number :");
   scanf("%d",&n);

   if(prime(n))
     printf("%d is prime\n",n);
   else
     printf("%d is not prime\n",n);
}

int prime(int n)
{
int i;
    for(i=2;i<=n/2;i++)
    {
      if(n%i==0)
       return 0; // Number is not prime
    }

    return 1; // No factor found, so prime number
}

Create a function that takes an array of 10 integers and returns sum of the array.

// Program to take an array of 10 numbers and to return sum of array

#include<stdio.h>

main()
{
   int a[]={12,23,44,55,33,343,13,34,335,22};  // initialize array

    printf("Sum = %d\n", sum_array(a) );
}

int sum_array(int a[10])
{
    int i,sum=0,n;

    for(i=0;i<10;i++)
      sum+=a[i];

    return sum;
}

Create a function that takes a string and a character and returns number of times the character is found in the string

// Create a function that returns how many times given char is present in the given string

#include<stdio.h>
int count_char(char s[20],char c);

main()
{
  int count;


   count = count_char("How are you",'o');
   printf("Count = %d\n",count);

}
int count_char(char s[20],char c)
{
    int count=0,i;

     for(i=0; s[i] != '\0'; i++)
     {
         if(s[i]== c)
          count++;
     }

     return count;
}

Create a function that takes an array of 10 integers and returns highest number in the array

 // Program to take an array of 10 numbers and to return highest number in array

#include<stdio.h>

main()
{
   int a[] = {33,11,32,32,12,43,83,31,12,34};
   int biggest;

    biggest=highest_number(a);
    printf("Highest number in the array is %d", biggest);
}

int highest_number(int a[10])
{
    int i,biggest;

    biggest=a[0];
    for(i=0;i<10;i++)
    {
       if(a[i]>biggest)
        biggest=a[i];
    }

    return biggest;
}

Create a function that takes two integers and returns GCD of the numbers

// Program to find GCD of 2 numbers using a function

#include<stdio.h>

void main()
{
   int a,b,g;

    printf("Enter two numbers : ");
    scanf("%d%d",&a,&b);

    g=gcd(a,b);

    printf("GCD of %d and %d is %d\n",a,b,g);

}
int gcd(int a,int b)
{
    int i, big;

     big = a < b ? a : b;

     for(i=big; i >=1 ; i--)
     {
         if(a % i ==0 && b % i == 0)
           return i;
     }
}

Create a function that takes an array of 10 integers and position of the element to be deleted, and delete the element from array. Fill last element of the array with 0.

// Program to delete the element at the given position from an array of 10 elements and fill the last element with 0

#include<stdio.h>

void main()
{
    int a[10],i,pos;

    srand(time(0)); // Initialize seed
    // Fill array with random numbers
    for(i=0;i<10;i++)
    {
      a[i] = rand() % 100;
      printf("%d\t", a[i]);
    }

    printf("\nEnter position of element to delete :");
    scanf("%d",&pos);

    delete_item(a,pos);

    printf("\nArray after deletion\n");

    for(i=0;i<10;i++)
      printf("%2d\t",a[i]);
}

void delete_item(int a[],int pos)
{
 int i;

    for(i=pos; i < 9; i++)
    {
      a[i]=a[i+1];
    }

    a[9]=0; // Set last element to 0
}

Lesson 15 - Pointers

Create a function to take two numbers (int) and set both of them to the highest of two.

// Create a function to set both the parameters to biggest of the two

void  set_big(int * p1, int * p2)
{
   if (*p1 > *p2)
      *p2 = * p1;
   else
      *p1 = * p2;
}

main()
{
  int a=30, b=20;

     set_big(&a,&b);
     printf("%d %d", a, b);
}

Create a function that takes an array of integers and sets all elements to zeros. Make function flexible so that it can work with an array of any size.

// Program to create a function that fills the given array with zeros
#include<stdio.h>
#include<string.h>

main()
{
    int a[10],b[20];

    zero_fill(a,10);
    zero_fill(b,20);

    // print arrays
    printf("\nFirst Array\n");
    print(a,10);
    printf("\nSecond Array\n");
    print(b,20);
}


void print(int a[], int size)
{
    int i;

      for(i=0; i < size; i ++)
         printf("%5d", a[i]);
}

void zero_fill(int a[], int size)
{
    int i;


     for(i=0; i < size ;i++)
     {
         a[i] = 0;
     }
}

Create a function that returns the number of uppercase and lowercase letters in the given string. Hint: Use pass by reference to return two values from a function.

/* Program to create a function that  returns the number of uppercase and lowercase letters in the given string*/
#include<stdio.h>
#include<string.h>

main()
{
    int upper,lower;
    char st[30];

     printf("\nEnter a string  : ");
     gets(st);

     count_upper_lower(st,&upper,&lower);

     printf("\nNumber of upper case letters : %d",upper);
     printf("\nNumber of lower case letters : %d",lower);
}

int count_upper_lower(char * st,int * upper, int * lower)
{
    int i;

     *upper = *lower = 0;

     for(i=0; st[i]!='\0';i++)
     {
         if(isupper(st[i]))
           (*upper)++;
         else
             if(islower(st[i]))
                (*lower)++;
     }
}

Write a program to find out how many times a substring is found in main string. Accept main string and sub string from keyboard.

/* Program to count how many times substring is present in main string */
#include<stdio.h>
#include<string.h>

main()
{
    int count=0;
    char  st[100], sub[20], *p;


     printf("\nEnter main string : ");
     gets(st);

     printf("\nEnter substring   : ");
     gets(sub);

     p = st; // make p point to main string
     while(1)
     {
         p = strstr(p,sub);
         if(p == NULL)
            break;

         count ++;
         p++;  // start next search after where previous occurrence was found
    }

    printf("\nSubstring [%s] was found [%d] time(s) in [%s]\n",sub,count,st);
}

Create a function to take two arrays of same size and copy second array to first array in reverse order.

// Program to create a function to take two arrays of same size and copy second array to first array in reverse order  

#include<stdio.h>

void arrayreverse(int *source, int * target);

main()
{
   int i;
   int a[10],b[10];

    // fill first array with random numbers
    srand(time(0)); // init random seed
    printf("\nElements in first array\n");
    for(i=0;i<10;i++)
    {
       a[i] = rand() % 100;
       printf("%5d",a[i]);
    }


    reverse_array(a,b);


    printf("\nElements in second array\n");
    for(i=0;i<10;i++)
      printf("%5d",b[i]);
}

void reverse_array(int *source ,int * target)
{
    int i,j;

     for(i=0,j=9;i<10;i++,j--)
     {
         target[j]= source[i];
     }

}

Lesson 16 - Structures

Create a structure to represent a product with id, name, price and quantity on hand. Read details from user and print all details along with net price, which includes a tax of 18%

// Program to create a structure to represent a product with id, name, price and quantity on hand.
// Read details from user and print all details along with net price, which includes a tax of 18%

#include<stdio.h>
struct product
{
    int id;
    char name[30];
    int quantity;
    float price;
};

void main()
{
    struct product p;
    float netprice;

     printf("Enter product id        :");
     scanf("%d",&p.id);
     fflush(stdin);  // we need to clear keyboard buffer to get rid of \n entered in previous scanf()
     printf("Enter product name      :");
     gets(p.name);
     printf(("Enter product quantity :"));
     scanf("%d",&p.quantity);
     printf("Enter product price     :");
     scanf("%f",&p.price);

     netprice= p.price*1.18;
	 
	 
     printf("Id         : %d\n",p.id);
     printf("Name       : %s\n",p.name);
     printf("Quantity   : %d\n",p.quantity);
     printf("Price      : %.2f\n",p.price);
     printf("NetPrice   : %.2f\n",netprice);

}

Create a function that takes two parameters of type struct product and return true if they match exactly, otherwise false.

// Create a function that takes two parameters of type struct product and return true (1)if they match exactly,
// otherwise false(0)

#include<stdio.h>

struct product
{
    int id;
    char name[30];
    int qty;
    float price;
};

int compare(struct product s,struct product p);

main()
{
    struct product p1 = {1,"iPhone X",10,80000};
    struct product p2 = {1,"iPhone X",10,80000};

    if ( compare(p1,p2)) // returns 1 (true) when two variables have same data
       printf("Equal\n");
    else
       printf("Not Equal\n");
}

int compare(struct product p1,struct product p2)
{
     if(p1.id == p2.id && strcmp(p1.name,p2.name) ==0 && p1.qty == p2.qty && p1.price == p2.price)
        return 1;
     else
        return 0;
}

Create a structure that stores time – hours, minutes, and seconds. Create an array of 5 elements of type struct time, read values from keyboard into array and then display them in HH:MM:SS format.

 /*Program to Create a structure that stores time – hours, minutes, and seconds and  an array of 5 elements of type struct time,
  read values from keyboard into array and then display them in HH:MM:SS format.*/

#include<stdio.h>

struct time
{
  int hours;
  int minutes;
  int seconds;
};

void main()
{
    struct time a[5];
    int i,j;

     for(i=0;i<5;i++)
     {
       printf("Enter time [hh:mm:ss] : ");
       scanf("%d:%d:%d",&a[i].hours, &a[i].minutes, &a[i].seconds);
     }


     for(i=0;i<5;i++)
     {
         printf("%02d:%02d:%02d\n",a[i].hours,a[i].minutes,a[i].seconds);
     }
}

Create a function that takes a parameter of type struct time and return time after adding 1 second.

// Program to create a function that takes a parameter of type struct time and return another struct time after adding 1 second
#include<stdio.h>
struct time
{
  int hours;
  int minutes;
  int seconds;
};
struct time add_second(struct time t);

void main()
{
  struct time t1 = {10,20,30}, t2;


   t2 = add_second(t1);
   printf("%02d:%02d:%02d",t2.hours,t2.minutes,t2.seconds);
}

struct time add_second(struct time t)
{
   t.seconds ++;
   if (t.seconds > 59)
   {
       t.seconds = 0;
       t.minutes++;
       if ( t.minutes > 59)
       {
           t.minutes = 0;
           t.hours ++;
           if(t.hours > 23)
             t.hours = 0;
       }
   }
   return t;
}

Lesson 17 - Text File Handling

Accept a filename and display all non-blank lines of the file.

// Display all non-blank lines from the given file
#include <stdio.h>

main()
{
  char line[100], filename[50];
  FILE * fp;


     printf("Enter filename  : ");
     gets(filename);

     fp = fopen(filename, "rt");

     if (fp == NULL)
     {
          printf("\nError : Could not open %s file. Quitting.", filename);
          exit(1);  // Exit program with error code
     }


     while(1)
     {
        if (fgets(line,100,fp) == NULL)  // if EOF
             break;

        // Length of line must be greater than 1 to be non-blank.
        // Line always contains new line (\n), so length is always a minimum of 1

        if (strlen(line) > 1)
            printf("%s",line);


     }
    fclose(fp);

}

Accept a filename and convert its contents to uppercase.

// Convert contents of file to uppercase
#include <stdio.h>

main()
{
  char line[100], filename[50];
  FILE * fp, * tfp;


     printf("Enter filename  : ");
     gets(filename);

     fp = fopen(filename, "rt");

     if (fp == NULL)
     {
          printf("\nError : Could not open %s file. Quitting.", filename);
          exit(1);  // Exit program with error code
     }

     tfp = fopen("tempfile.txt", "wt");

     if (tfp == NULL)
     {
          printf("\nError : Could not create target file - tempfile.txt. Quitting.");
          exit(1);  // Exit program with error code
     }

     while(1)
     {
        if (fgets(line,100,fp) == NULL)  // if EOF
             break;

        fputs(strupr(line),tfp);  // Convert to upper and write to target
     }
     fclose(fp);
     fclose(tfp);

     // Delete source file
     remove(filename);
     rename("tempfile.txt",filename);
}

Accept a filename and display number of chars, words and lines in the file.

// Program to count no. of chars, words and lines in the given file
#include <stdio.h>

main()
{
  FILE * fp;
  char filename[50];
  int ch,chars,words,lines, inword;

     printf("Enter filename  : ");
     gets(filename);

     fp = fopen(filename, "rt");

     if (fp == NULL)
     {
          printf("\nError : Could not open %s file. Quitting.", filename);
          exit(1);  // Exit program with error code
     }

     chars = words = lines = 0;
     inword = 0;
     while(1)
     {
       ch = fgetc(fp);
       if (ch == -1)
          break;

       chars ++;

       if(ch == '\n')
       {
          lines ++;
          inword = 0;  // not in word as we are at the beginning of next line
       }
       else
         if (!isspace(ch))  // not a space
         {
           if(!inword)   // not in words, so first char in new word, increment word count
           {
              inword = 1;
              words++;
           }
         }
         else   // space
           inword = 0;
    }

    fclose(fp);

    printf("\nChars = %d, Words = %d, Lines = %d", chars, words, lines);

}

Assume a file marks.txt, which contains marks of students one per line. Display marks that are >= average marks.

// Program to take a file which contains marks of students one per line and display marks that are >= average marks 

#include <stdio.h>

main()
{
  FILE * fp;
  char line[5];
  int total, count, avg, marks;

     fp = fopen("marks.txt", "rt");
     if (fp == NULL)
     {
          printf("\nError : Could not open MARKS.TXT. Quitting.");
          exit(1);  // Exit program with error code
     }

     count = 0;
     while(1)
     {
        if (fgets(line,5,fp) == NULL)
             break;
        total +=  atoi(line);
        count ++;
     }

     avg = total / count;

     fclose(fp);

     // Reopen file. A better way is to use fseek()
     fp = fopen("marks.txt", "rt");

     printf("\nMarks that are greater than average marks - %d\n",avg);

     while(1)
     {
        if (fgets(line,5,fp) == NULL)
             break;
        marks = atoi(line);
        if ( marks > avg)
             printf("%d\n",marks);
     }

}

Accept a filename and encrypt (add a number to ASCII code of each character) file and write encrypted content into another file with same primary filename, but .enc extension.

// Program to encrypt file and write into another file with .enc extension

#include <stdio.h>

void main()
{
  FILE * fp, * tfp;
  char filename[50], targetfilename [50];
  int ch;

     printf("Enter filename : ");
     gets(filename);

     fp = fopen(filename, "rt");
     if (fp == NULL)
     {
          printf("\nError : Could not open file %s. Quitting.", filename);
          exit(1);  // Exit program with error code
     }

     // create target file
     strcpy(targetfilename,filename);
     strcat(targetfilename,".enc");

     tfp = fopen(targetfilename, "wb");  // open in binary mode, more in next lesson
     if (tfp == NULL)
     {
          printf("\nError : Could not create file %s. Quitting.", targetfilename);
          exit(1);  // Exit program with error code
     }

     while(1)
     {
        ch = fgetc(fp);
        if(ch == EOF)
             break;
        fputc(ch + 1, tfp);  // add 1 to ASCII code of char to make it illegible
     }

     fclose(fp);
     fclose(tfp);
}

Lesson 18 - Binary File Handling

Create a file called marks.dat and write marks of students based on admission number. Marks of admno 1 will be written in first 4 bytes of file and then marks of admno 2 and so on. Accept marks from user in the order of admission number. Stop taking input when user enters -1.

 // Program to write marks into marks.dat

#include <stdio.h>
#define  FILENAME  "marks.dat"

void main()
{
  FILE * fp;
  int marks;

     fp = fopen(FILENAME,"wb");
     if ( fp == NULL)
     {
         printf("Sorry! File could not be opened!\n");
         return;
     }

     while(1)
     {
       printf("Enter marks [-1 to stop] : ");
       scanf("%d",&marks);

       if (marks == -1)
          break;

       fwrite(&marks,sizeof(int),1,fp);
    }
    fclose(fp);
}

Open marks.dat and display marks of student based on the given admission number. Hint: Use fseek() to position file pointer at the required position, based on admission number, before reading marks.

// Program to display marks for the given admno

#include <stdio.h>
#define  FILENAME  "allmarks.dat"

void main()
{
  FILE * fp;
  int marks, admno, count;

     fp = fopen(FILENAME,"rb");
     if ( fp == NULL)
     {
         printf("Sorry! File could not be opened!\n");
         return;
     }

     while(1)
     {
       printf("Enter admno [0 to stop] : ");
       scanf("%d",&admno);

       if (admno == 0)
          break;

       //Go to required position based on admno
       fseek(fp,(admno - 1) * sizeof(int), SEEK_SET);
       count = fread(&marks,sizeof(int),1,fp);
       if (count == 1)
           printf("\nMarks = %d\n",marks);
       else
           printf("\nSorry! Couldn't read marks!\n");
    }

    fclose(fp);
}

Accept two binary files and merge them into target file. Accept names of source files and target file from user.

// Merge two files and copy into another

#include <stdio.h>

FILE * open(char *, char *);  // Prototype for function

void main()
{
  char sfn1[50], sfn2[50], tfn[50];
  FILE * sfp1, * sfp2, * tfp;
  char buffer[100];
  int count;

     printf("Enter first source filename  : ");
     gets(sfn1);
     sfp1 = open(sfn1,"rb");

     printf("Enter second source filename : ");
     gets(sfn2);
     sfp2 = open(sfn2,"rb");

     printf("Enter target filename        : ");
     gets(tfn);
     tfp = open(tfn,"wb");

     // copy first source file to target
     while(1)
     {
         count = fread(buffer,1,100,sfp1); // read a block of 100 bytes
         if (count == 0)  // stop if we reached end of file
             break;
         // write buffer to target file
         fwrite(buffer,1,count,tfp);  // write whatever bytes read from source to target
    }
    fclose(sfp1);

    // copy second source file to target
    while(1)
    {
         count = fread(buffer,1,100,sfp2);
         if (count == 0)
             break;
         // write buffer to target file
         fwrite(buffer,1,count,tfp);
    }

    fclose(sfp2);
    fclose(tfp);
}

FILE * open(char * filename, char * mode)
{
    FILE * fp;

      fp = fopen(filename, mode);

      if (fp == NULL)
      {
          printf("\nError : Could not open %s file. Quitting.", filename);
          exit(1);  // Exit program with error code
      }

      return fp;
}

Lesson 19 - Miscellaneous Topics - Part 1

Create a macro that takes an int and returns true if it is even number

// Create a macro that takes an int and returns true if it is even number

#define iseven(n)  n % 2 == 0

void main()
{
  int n = 11;

    printf("%s", iseven(n) ? "Even" : "Odd");
}

Create a macro that takes a year and returns true if it is a leap year

// Create a macro to test leap year

#define leapyear(y)  y % 4 == 0 && y % 4 != 100 || y % 400 == 0

void main()
{
int year;

   // print leap years from 2000 to 2020
   for( year = 2000; year <= 2020; year ++)
   {
      if (leapyear(year))
         printf("%d\n", year);
   }

}

Create enumeration that represents days of a week and use it in a switch statement to calculate wage. Wage depends on day of the week as follows: Mon – 1000, Tue – 1000, Wed – 1000, Thu – 1200, Fri – 1200, Sat – 1500, Sun – 1500

// Wage calculation based on day of week

enum week
{
    MON, TUE, WED, THU, FRI,SAT,SUN
};

void main()
{
 enum week dayofweek;
 int wage;

    printf("Enter day of week  [0-6] : ");
    scanf("%d",&dayofweek);

    switch(dayofweek)
    {
    case MON:
    case TUE:
    case WED:
        wage = 1000; break;
    case THU:
    case FRI:
        wage = 1200; break;
    case SAT:
    default :
        wage = 1500;
    }

    printf("Wage = %d\n",wage);
}

Lesson 20 - Miscellaneous Topics - Part 2

Accept a filename on command line and display how many alphabets, digits and special characters the file has.

// Count Alphabets, digits and other chars in a file
#include <stdio.h>

main(int argc, char * argv[])
{
  FILE * fp;
  int ch, alphas, digits, others;

     if(argc == 1)  // No parameters passed
     {
         printf("\nMissing filename!\n");
         printf("\nUsage : count <filename>\n");
         return;
     }

     fp = fopen(argv[1],"r");
     if ( fp == NULL)
     {
       printf("Sorry! File not found. Quitting.");
       return;
     }

     alphas = digits = others = 0;
     while(1)
     {
        ch = fgetc(fp);
        if (ch == EOF)
          break;

        if(isalpha(ch))
           alphas++;
        else
         if (isdigit(ch))
           digits ++;
         else
           others++;
     }

     fclose(fp);

     printf("No. of Alphabets  : %d\n",alphas);
     printf("No. of Digits     : %d\n",digits);
     printf("No. of Other chars: %d\n",others);

}

Create a recursive function that takes number and prints digits in reverse order

// Program to print digits of a number in reverse order using recursion

#include <stdio.h>

void print_reverse(int num)
{
  if (num == 0)
     return;

  printf("%d", num % 10); // print rightmost digit
  print_reverse(num/10);  // remove rightmost digit and make recursive call

}

void main()
{
  print_reverse(1234);
}

Display sum of all numbers given as command line arguments

// Program to display sum of numbers given on command line

#include <stdio.h>

void main(int argc, char * argv[])
{
  int sum = 0,i;

     for(i=1; i < argc; i ++)
     {
         sum +=  atoi( argv[i]);
     }
     printf("Sum = %d",sum);
}

Accept number of students in a class and then take marks for all students. Display all marks in sorted order.

// Take marks and print them in sorted order using dynamic memory allocation

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void main()
{
 int * marks, count, i,j, temp;

     printf("Enter no. of students :");
     scanf("%d",&count);

     srand(time(0));
     // Allocate a block to accommodate marks
     marks = (int *) malloc(sizeof(int) * count);
     if (marks == NULL)
     {
         printf("Sorry! Memory allocation error. Quitting.");
         return;
     }

     // Take input from user
     for(i=0; i < count ; i ++)
     {
        // printf("Enter marks for student with roll no %d :", i + 1);
        // scanf("%d", marks + i);
        marks[i] = rand() % 100;
     }

     // Sort marks
     for(i=0; i < count -1 ; i ++)
     {
      for(j=i+1; j < count; j ++)
      {
          if ( marks[i] > marks[j])
          {
             temp = marks[i];
             marks[i] = marks[j];
             marks[j]  = temp;
          }
      }
     }

     // Print sorted marks
     for(i=0; i < count ; i ++)
     {
        printf("%5d\n",marks[i]);
     }

}