I can not determine if it is a prime number - c

Question

The below program correctly outputs the divisors of the input numbers, but it does not correctly report whether the inputs are prime. For example, when the input is 13, it does not print "The number you entered is a prime number." What's wrong with it?
#include <stdio.h>
#include <stdbool.h>
int main(void)
{
int num;
bool isPrime = true;
printf("Enter a number: ");
while (scanf("%d", &num) == 1)
{
for (int i = 2; i * i <= num; ++i)
{
if (num % i == 0)
{
if (i * i != num)
{
printf("%d ve %d, divides %d\n", i, num / i, num);
}
else
{
printf("%d divides %d.\n", i, num);
}
isPrime = false;
}
}
}
if (isPrime)
{
printf("The number you entered is a prime number.");
}
return 0;
}

Answer 1

the reason is that scanf is in a while loop if there's a valid input but you are checking & printing if it's prime outside of the loop... if you expect this program just get one input and validate it once, then you just need to change that while to if:
#include <stdio.h>
#include <stdbool.h>
int main(void)
{
int num;
bool isPrime = true;
printf("Enter a number: ");
if (scanf("%d", &num) == 1)
{
for (int i = 2; i * i <= num; ++i)
{
if (num % i == 0)
{
if (i * i != num)
{
printf("%d ve %d, divides %d\n", i, num / i, num);
}
else
{
printf("%d divides %d.\n", i, num);
}
isPrime = false;
}
}
}
if (isPrime)
{
printf("The number you entered is a prime number.");
}
return 0;
}
If you expect this program goes in a loop to keep on getting input and validating if it's prime or not, this should do the job:
#include <stdio.h>
#include <stdbool.h>
int main(void)
{
int num;
bool isPrime = true;
while (1)
{
isPrime=true;
printf("Enter a number: ");
if (scanf("%d", &num) == 1)
{
for (int i = 2; i * i <= num; ++i)
{
if (num % i == 0)
{
if (i * i != num)
{
printf("%d ve %d, divides %d\n", i, num / i, num);
}
else
{
printf("%d divides %d.\n", i, num);
}
isPrime = false;
}
}
}
if (isPrime)
{
printf("The number you entered is a prime number.\n");
}
}
return 0;
}

Answer 2

You have missed 2 things !
You should have printed inside the while loop !
In addition to that you didn't change the status of isPrime=true; !
Hope this answers your question !
#include <stdio.h>
#include <stdbool.h>
int main(void)
{
int num;
bool isPrime = true;
while (scanf("%d", &num) == 1)
{
for (int i = 2; i * i <= num; ++i)
{
if (num % i == 0)
{
if (i * i != num)
{
printf("%d ve %d, divides %d\n", i, num / i, num);
}
else
{
printf("%d divides %d.\n", i, num);
}
isPrime = false;
}
}
if (isPrime)
{
printf("The number you entered is a prime number.\n");
}
isPrime=true;
}
return 0;
}

Answer 3

When you entered a prime number, your while loop doesn't break. Try it:
#include <stdio.h>
#include <stdbool.h>
int main(void) {
int num;
bool isPrime = true, finishIt = false;
printf("Enter a number: ");
while (1) {
while (1) {
if (scanf("%d", &num) != 1)
continue;
if (num == 0) {
finishIt = true;
break;
}
int i;
for (i = 2; i * i <= num; ++i) {
if (num % i == 0) {
if (i * i != num) {
printf("%d ve %d, divides %d\n", i, num / i, num);
} else {
printf("%d divides %d.\n", i, num);
}
isPrime = false;
}
}
if (i * i >= num)
break;
}
if (isPrime) {
printf("The number you entered is a prime number.");
}
isPrime = true;
if (finishIt)
break;
}
return 0;
}