Primes less than an integer - c

Question

I wrote a program to find all primes less that a user-input integer. However, it just hangs. I assume using all these continues and whatnot is a mess and I have made spaghetti code...can anyone help me?
/*takes integer input, displays all primes less than that integer*/
#include <stdio.h>
int main(void) {
unsigned int num_in, test_num = 0, divisor = 0;
_Bool primestate = 0;
printf("Please enter an integer.\n");
scanf("%d", &num_in);
while(test_num < num_in) {
while(divisor < test_num) {
if(test_num % divisor == 0) {
primestate = 1;
}
test_num++;
}
if(primestate == 1) {
printf("%d is prime and less than %d.\n", test_num, num_in);
} else {
continue;
}
}
return 0;
}

Answer 1

You never increment test_num or divisor, so it gets stuck in one of the loops.
while(test_num < num_in) {
while(divisor < test_num) {
if(test_num % divisor == 0) {
primestate = 1;
}
divisor++; // NEW LINE
}
if(primestate == 1) {
printf("%d is prime and less than %d.\n", test_num, num_in);
} else {
continue;
}
test_num++; // NEW LINE
}
You also have a possible division by 0 (when divisor equals 0) on this line:
if(test_num % divisor == 0) {

Answer 2

#include <stdio.h>
#include <stdbool.h>
int main(void) {
unsigned int num_in, test_num, divisor;
bool primestate;
printf("Please enter an integer.\n");
scanf("%u", &num_in);
if(2 < num_in)
printf("\n%u\n", 2);
for(test_num = 3; test_num < num_in; test_num += 2){
primestate = true;
for(divisor=3; divisor * divisor <= test_num ; divisor += 2) {
if(test_num % divisor == 0) {
primestate = false;
break;
}
}
if(primestate) {
printf("%u\n", test_num);
}
}
return 0;
}