C Program to Check Number is prime or Not prime

                                      C Program 

 C Program to Check Number is prime or Not prime

Examples :-

#include<stdio.h>

#include<conio.h>

void main()

{

int a, i, flag=0;

printf("enter a positive integer");

scanf("%d", &a);

if(a==0||a==1)

flag=1;

for(i=2;i<=a/2;i++)

{

if(a%i==0)

{

flag =1;

break;

}

}

if (flag==0)

printf("%d is prime number ", a);

else

printf("%d is not prime number",a);

getch();

return 0;

}

C Program to Check Number is prime or Not prime

Explain Program

Step :1

#include <stdio.h>

 Standard Input Output library, which is required for functions like printf() and scanf().

Step :2

void main()

This is the main function, where program execution starts.

Step :3

int a, i, flag = 0;

 stores the number  a, b entered by the user.

Step :4

printf ("enter a positive integer");

scanf ("%d", &a);

 user to enter a number.

 scanf () reads the input and stores it in variable a.

Step :5

if (a == 0 || a == 1)

    flag=1;

0 and 1 are not prime numbers by definition.

Step :6

for (i = 2; i <= a / 2; i++)

{

    if (a % i == 0)

    {

        flag = 1;

        break;

    }

}

loop check if any number between 2 and a/2 divides a completely

Step :7

if (flag == 0)

    printf("%d is prime number ", a);

else

    printf("%d is not prime number", a);

If no divisor was found (flag is still 0), the number is prime.

Output 

 enter a positive integer 133
   133 is not prime number

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