#include <stdio.h>
main() { int n, i, c = 0; printf("Enter any number n:"); scanf("%d", &n); //logic for (i = 1; i <= n; i++) { if (n % i == 0) { c++; } } if (c == 2) { printf("n is a Prime number"); } else { printf("n is not a Prime number"); } return 0;
}
Program Output:

int isPrime(long long number) {	if (number == 0 || number == 1 || (number % 2 == 0 && number > 2)) {	return 0;	}	else {	for (long long i=3; i <= (long long)sqrt(number)+1; i++) {	if (number % i == 0) {	return 0;	}	}	return 1;	}
}

#include <stdio.h>
int main() { int n, i, flag = 0; printf("Enter a positive integer: "); scanf("%d", &n); if (n == 0 || n == 1) flag = 1; for (i = 2; i <= n / 2; ++i) { if (n % i == 0) { flag = 1; break; } } // flag is 0 for prime numbers if (flag == 0) printf("%d is a prime number.", n); else printf("%d is not a prime number.", n); return 0;
}

int n=7,i,flag=0;	for(i=2;i<n/2;i++){	if(n%i==0){	flag=1;	break;	}	}	if(flag==0){	printf("Prime number");	}else{	printf("not prime number");	}