C Program to Check Whether a Number is Prime or Not

In this tutorial, i am going to show you how to check whether a number is prime or not with the help of for loop, while loop, and function.

A number that’s only divisible by 1 and itself is named a Prime Number. For Example, 3, 5, 7, 11 are Prime Numbers.

Programs to Check Whether a Number is Prime or Not in C

• Algorithm to Check a Number is Prime or Not
• C Program to Check Prime Number Using For Loop
• C Program to Check Prime Number Using While Loop
• C Program to Check Prime Number Using Function

Algorithm to Check a Number is Prime or Not

Follow the below given algorithm to write a program to check a number is prime or not; as follows:

Step 1: Start
Step 2: Read number n
Step 3: Set f=0
Step 4: For i=2 to n-1
Step 5: If n mod 1=0 then
Step 6: Set f=1 and break
Step 7: Loop
Step 8: If f=0 then
         print 'The given number is prime'
        else
         print 'The given number is not prime'
Step 9: Stop

C Program to Check Prime Number Using For Loop

#include <stdio.h>
 
int main()
{
  int i, Number, count = 0; 
   
  printf("\n Please Enter any number to Check for Prime :- ");
  scanf("%d", &Number);
 
  for (i = 2; i <= Number/2; i++)
   {
     if(Number%i == 0)
     {
        count++;
	break;
     }	
   }
   if(count == 0 && Number != 1 )
   {
   	printf("\n %d is a Prime Number", Number);
   }
   else
   {
   	printf("\n %d is Not a Prime Number", Number);
   }
  return 0;
}

The result of the above c program; as follows:

Please Enter any number to Check for Prime :- 10
10 is Not a Prime Number

C Program to Check Prime Number Using While Loop

#include <stdio.h>
 
int main()
{
  int i = 2, Number, count = 0; 
   
  printf("\n Please Enter any number to Check for Prime :- ");
  scanf("%d", &Number);
 
  while(i <= Number/2)
   {
     if(Number%i == 0)
     {
        count++;
	break;
      }
      i++;	
   }
   if(count == 0 && Number != 1 )
   {
   	printf("\n %d is a Prime Number", Number);
   }
   else
   {
 	printf("\n %d is Not a Prime Number", Number);
   }
  return 0;
}

The result of the above c program; as follows:

Please Enter any number to Check for Prime :- 11
11 is a Prime Number

C Program to Check Prime Number Using Function

#include <stdio.h>
int Find_Factors(int Number)
{ 
  int i, Count = 0; 
  
  for (i = 2; i <= Number/2; i++)
   {
    if(Number%i == 0)
     {
       Count++;
     } 
   }
   return Count;
}
 
int main()
{
  int Number, count = 0; 
   
  printf("\n Please Enter any number to Check for Prime :- ");
  scanf("%d", &Number);
 
  count = Find_Factors(Number);
   if(count == 0 && Number != 1 )
   {
   	printf("\n %d is a Prime Number", Number);
   }
   else
   {
   	printf("\n %d is Not a Prime Number", Number);
   }
  return 0;
}

The result of the above c program; as follows:

Please Enter any number to Check for Prime :- 31
31 is a Prime Number

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