Prime Number or Not in C Program using While, Do-while, For loop, and Function

Prime number or not in c program.

In this article, you will learn how to check whether the given input number is a prime number or not a prime number.

To solve this problem we will use the various approaches like while loop, do-while loop, for loop, function, etc.

Example-1

Example-2

You should know about the following topics in C programming to understand this program:

• If-else statement
• For loop in C
• While loop in C
• Do-while loop in C
• Function in C

1 - Prime Number or Not in C using While loop

// Prime Number or Not in C using While loop
#include <stdio.h>

// It's the main function of the program
int main()
{
    int num;
    int is_prime = 0;

    // Step-1 Take input from the User
    printf("INPUT A NUMBER: ");
    scanf("%d", &num);

    // Step-2 Check if the input number is less than or equal to 1
    if (num <= 1)
        is_prime = 1;

    // Step-3 Use a loop to check whether the input number is prime or not
    int i = 2;
    while (i <= num / 2)
    {
        // If the input number is divisible by i, then the input number is not a Prime
        if (num % i == 0)
        {
            is_prime = 1;
            break;
        }
        i++;
    }

    // Step-4 If `is_prime == 0` INPUT number is prime
    // Final output of the program
    if (is_prime == 0)
        printf("%d IS A PRIME NUMBER.\n", num);
    else
        printf("%d IS NOT A PRIME NUMBER.\n", num);

    return 0;
}

Run

Output

2 - Prime Number or Not in C using Do-while loop

// Prime Number or Not in C using Do-while loop
#include <stdio.h>

// It's the main function of the program
int main()
{
    int num;
    int is_prime = 0;

    // Step-1 Take input from the User
    printf("INPUT A NUMBER: ");
    scanf("%d", &num);

    // Step-2 Check if the input number is less than or equal to 1
    if (num <= 1)
        is_prime = 1;

    // Step-3 Use a loop to check whether the input number is prime or not
    int i = 2;
    do
    {
        // If the input number is divisible by i, then the input number is not a Prime
        if (num % i == 0)
        {
            is_prime = 1;
            break;
        }
        i++;
    } while (i <= num / 2);

    // Step-4 If `is_prime == 0` INPUT number is prime
    // Final output of the program
    if (is_prime == 0)
        printf("%d IS A PRIME NUMBER.\n", num);
    else
        printf("%d IS NOT A PRIME NUMBER.\n", num);

    return 0;
}

Run

3 - Prime Number or Not in C using For loop

// Prime Number or Not in C using For loop
#include <stdio.h>

// It's the main function of the program
int main()
{
    int num;
    int is_prime = 0;

    // Step-1 Take input from the User
    printf("INPUT A NUMBER: ");
    scanf("%d", &num);

    // Step-2 Check if the input number is less than or equal to 1
    if (num <= 1)
        is_prime = 1;

    // Step-3 Use a loop to check whether the input number is prime or not
    for (int i = 2; i <= num / 2; i++)
    {
        // If the input number is divisible by i, then the input number is not a Prime
        if (num % i == 0)
        {
            is_prime = 1;
            break;
        }
    }

    // Step-4 If `is_prime == 0` INPUT number is prime
    // Final output of the program
    if (is_prime == 0)
        printf("%d IS A PRIME NUMBER.\n", num);
    else
        printf("%d IS NOT A PRIME NUMBER.\n", num);

    return 0;
}

Run

Output

4 - Prime Number or Not in C using Function

// Prime Number or Not in C using For loop
#include <stdio.h>

// Function to check if it is a prime or not
int is_prime(int num)
{
    // If the input number is divisible by i, then the input number is not a Prime
    for (int i = 2; i < num; i++)
    {
        // If the input number is divisible by i, It's not a prime number
        if (num % i == 0)
            return 0;
    }

    // If there are no divisors, It's a prime number
    return 1;
}

// It's the main function of the program
int main()
{
    int num;

    // Step-1 Take input from the User
    printf("INPUT A NUMBER: ");
    scanf("%d", &num);

    // Step-2 Check if the input number is less than or equal to 1
    if (num <= 1)
        printf("%d IS NOT A PRIME NUMBER.\n", num);
    else
    {
        // Step-3 Call the is_prime() function to check whether the input number is prime or not
        if (is_prime(num))
            printf("%d IS A PRIME NUMBER.\n", num);
        else
            printf("%d IS NOT A PRIME NUMBER.\n", num);
    }

    return 0;
}

Run

Output