C Program to Check Whether a Number is Prime or Not

August 26, 2019

Write C Program to find number is Prime number or not.

In this program we will find a number is a prime number or not with the help of for loop or if else statement. A number is considered as prime number when it satisfies the below conditions.

Prime number is a number which can be divided by 1 and itself
A number which can not be divided by any other number other than 1 or itself is a prime number.
It should have only 2 factors. They are, 1 and the number itself.

Ex- Number is 13. it have only 2 factor

it is divisible by 1.
And it is divisible by itself

So it is a prime number

Working:-

Step 1.Read a “num” value to check prime or not.
Step 2.set i=1,div=0.
Step 3.if i<=num if true go to step 4, else go to step 7.
Step 4.Check the condition num%i==0 if true then evaluate step 5, else go to step 6.
Step 5.set div=div+1
Step 6.i=i+1, go to step 4
Step 7.check div, if div==2 display prime, else display not prime
Step 8.Stop

C Program:-

#include<stdio.h>
int main()
{
      //initializing variables
      int c,number,div=0;

      //user input
      printf("Enter number: "); 
      scanf("%d",&number); 

      //checking for number of divisor
      for(c=1;c<=number;c++) 
      {
           if(number%c==0)
           {
                div++; 
            }
      }
      //no divisors other than 1 and itself
       if(div==2) 
       {
           //display
            printf("%d is a prime number",number);
       }
       else
       {
           //display
            printf("%d is not a prime number",number);
       }
    return 0;
}

Output:-

Enter number:6
6 is not a prime number

Enter number:13
13 is a prime number

Please Login/Signup to comment