TheAlgorithms-C/math/prime.c

/**
 * @file
 * @brief Program to identify if a number is [prime
 * number](https://en.wikipedia.org/wiki/Prime_number) or not
 */
#include <assert.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>

/**
 * Check if a given number is prime number or not
 * @param x number to check
 * @return `true` if given number is prime number, otherwise `false`
 */
bool isPrime(int x)
{
    if (x == 2)
    {
        return true;
    }
    if (x < 2 || x % 2 == 0)
    {
        return false;
    }

    double squareRoot = sqrt(x);

    for (int i = 3; i <= squareRoot; i += 2)
    {
        if (x % i == 0)
        {
            return false;
        }
    }
    return true;
}

/**
 * Test function
 * @return void
 */
void test()
{
    /* all the prime numbers less than 100 */
    int primers[] = {2,  3,  5,  7,  11, 13, 17, 19, 23, 29, 31, 37, 41,
                     43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97};
    for (size_t i = 0, size = sizeof(primers) / sizeof(primers[0]); i < size;
         ++i)
    {
        assert(isPrime(primers[i]));
    }

    /* Example Non-prime numbers */
    int NonPrimers[] = {-1, 0, 1, 4, 6, 8, 9, 10};
    for (size_t i = 0, size = sizeof(NonPrimers) / sizeof(NonPrimers[0]);
         i < size; ++i)
    {
        assert(!isPrime(NonPrimers[i]));
    }
}

/**
 * Driver Code
 * @return None
 */
int main()
{
    test();
    return 0;
}