Program to check a number for prime in C using function

Logic:

• Prime Number A number is prime if it is divisible by 1 and the number itself only.
• Enter the number n
• Example 1: n=15
• We will check whether number is divisible by any number from 2 to n-1 here 14.
• If it is divisible by any number (example 15 is divisible by 3) , then It is not prime number. And We dnt need to check further divisibility from 4 to 14.
• Example 2: n=5
• We will check whether number is divisible by any number from 2 to n-1 here 4.
• Since 5 is not divisible by any numbers 2, 3, 4 . So It is a prime number.

Algorithm

1. Enter the number as n
2. for(i=2;i<=n-1;i++)
3. {
4. if(n%i==0)
5. {
6. printf(“It is not prime”);
7. break;
8. }
9. }
10. if(i==n)
11. printf(“It is prime”);

Time Complexity: O(n)

Space Complexity: O(1)

Program

#include <stdio.h>
char check_prime(int n);
int main()
{
    printf("******************************************************\n");
    printf("******************************************************\n");
    printf("**  WAP to check a number for prime using function  **\n");
    printf("**          Created by Sheetal Garg                 **\n");
    printf("**          Assistant Professor                     **\n");
    printf("**          Phone No:9467863365                     **\n");
    printf("******************************************************\n");
    printf("******************************************************\n");
    int n;
    char result;
    printf("\nenter number\n");
    scanf("%d", &n);
    result = check_prime(n);
    if (result == 'T')
        printf("\nIt is prime");
    else
        printf("\nIt is not Prime");
    return 0;
}
char check_prime(int n)
{
    int i;
    for (i = 2; i <= n - 1; i++)
        if (n % i == 0)
            return 'F';
    return 'T';
}

Output 1

******************************************************
******************************************************
**  WAP to check a number for prime using function  **
**          Created by Sheetal Garg                 **
**          Assistant Professor                     **
**          Phone No:9467863365                     **
******************************************************
******************************************************

enter number
5

It is prime

Output 2

******************************************************
******************************************************
**  WAP to check a number for prime using function  **
**          Created by Sheetal Garg                 **
**          Assistant Professor                     **
**          Phone No:9467863365                     **
******************************************************
******************************************************

enter number
15

It is not prime