# C Program to Check given Number is Prime or Not | Prime Number program in C

### What is Prime Number :

• A Prime Number can be divided evenly only by 1, or itself.
• A Prime Number must be a whole number greater than 1.

#### Example:

• 3 can only be divided evenly by 1 or 3, so it is a prime number.
• But 6 can be divided evenly by 1, 2, 3 and 6 so it is NOT a prime number.

### Description :

This program accept one Integer from user and checks if it is prime or not. I am using one flag variable and setting that flag to 1 if given number is evenly dividable by any number (except 1 and given number). that’s why my for loop is started with 2 and ended at n/2

Note : There are other efficient ways to write this program. we will discuss them in next posts.

### Prime Number Program in C :

1. #include<stdio.h>
2. void main()
3. {
4.         int FLAG,i,num;
5.         // first set the flag to 0
6.         FLAG = 0;
7.         printf(“Enter any positive Number : “);
8.         scanf(“%d”,&num);
9.         for(i=2;i<num/2 ; i++)
10.         {
11.                 if(num%== 0)
12.                 {
13.                         FLAG=1;
14.                         break;
15.                 }
16.         }
17.         // check if FLAG is 0 or 1
18.         // if FLAG is 0 then Number is Prime.
19.         // otherwise Number is not Prime.
20.         if(FLAG == 0)
21.                 printf(“%d is Prime Number  n,num);
22.         else
23.                 printf(“%d is not a prime Number n,num);
24. } Venkat

Hi Guys, I am Venkatesh. I am a programmer and an Open Source enthusiast. I write about programming and technology on this blog.