(Arithmetic exercises) - square root method to Get Prime Number

"Algorithm notes" P162
on topic mathematical algorithm, in essence, is a math problem?
Code:

#include <stdio.h>
#include <math.h>
//判断是否为素数 
bool isPrime(int n){
	if(n <= 1) return false;
	int sqr = (int)sqrt(1.0*n);
	for(int i = 2;i <= sqr;i++){
		if(n % i == 0) return false;
	}
	return true;
}
//输出1000以内的素数 
int record[1010];
int signal = 0;
void findsushu(){
	for(int i = 0;i <1000;i++){
		if(isPrime(i) == true){
			record[signal++] = i;
		}
	}
}

int main(){
	findsushu();
	for(int i = 0;i <signal;i++){
		printf("%d ",record[i]);
	}
}