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Implementation of isPrimeNumber(int) Function

To implement an isPrimeNumber(int) function in C that checks whether an integer is a prime number (a number greater than 1 that has no positive divisors other than 1 and itself), you can create a function that iterates through potential divisors. Here's an example of how to implement the isPrimeNumber() function:

Example:


#include <stdio.h>

// Function to check if an integer is a prime number
int isPrimeNumber(int num) {
    // Handle special cases
    if (num <= 1) {
        return 0; // 0 and 1 are not prime numbers
    }

    // Check for divisors from 2 to the square root of num
    for (int i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            return 0; // Found a divisor, not a prime number
        }
    }

    return 1; // No divisors found, it's a prime number
}

int main() {
    int number1 = 17; // Prime number
    int number2 = 15; // Not a prime number

    if (isPrimeNumber(number1)) {
        printf("%d is a prime number.\n", number1);
    } else {
        printf("%d is not a prime number.\n", number1);
    }

    if (isPrimeNumber(number2)) {
        printf("%d is a prime number.\n", number2);
    } else {
        printf("%d is not a prime number.\n", number2);
    }

    return 0;
}

In this example:

  • The isPrimeNumber() function takes an integer num as its parameter.
  • It handles special cases: if num is less than or equal to 1, it returns 0 because 0 and 1 are not prime numbers.
  • The function then checks for divisors of num by iterating from i = 2 up to the square root of num. If it finds any divisor (i.e., num % i == 0), it returns 0 because num is not prime.
  • If no divisors are found, the function returns 1, indicating that num is a prime number.
  • In the main() function, two numbers (17 and 15) are checked using the isPrimeNumber() function, and the result is printed.

Output:


17 is a prime number.
15 is not a prime number.

You can use this isPrimeNumber() function to check whether any integer is a prime number by passing it as an argument to the function.

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