ewce09.azraftaohid.me/L2T1/CSE 278/Practices/w05/prime.c

#include <stdio.h>

void main() {
	int input;

	printf("Enter an integer: ");
	scanf("%d", &input);

	if (input == 0) {
		printf("0 is neither prime nor composite.");
		return;
	}

	if (input == 1) { // a prime number must have exactly 2 factors; 1 has only one
		printf("1 is not a prime number.");
		return;
	}

	if (input < 0) {
		printf("Negative numbers are not prime number.");
		return;
	}
	
	int i = 2;
	int limit = input / 2;
	for (; i <= limit; i++) {
		if (input % i == 0) {
			i = -1;
			break;
		}
	}

	if (i == -1) printf("%d is not a prime number.", input);
	else printf("%d is a prime number.", input);
}