问Euler问题3-我需要帮助来处理这一小段C

EN

#include <stdio.h>
#include <stdbool.h>  //This is to bring in the define of true
#include <math.h>  //This is to bring in the define of sqrt()

int LargestFactor (long number);
bool IsItPrime (int number);

int main (int argc, const char * argv[]) {
    long number;
    number = 600851475143;
    printf("The largest prime factor of %ld is %d.", number, LargestFactor(number));
}


int LargestFactor (long number) {
    int divider,i=1;
    bool foundIt=false;
    while (foundIt == false) {
        i++;
        if (number % i == 0 && IsItPrime(number/i)) {
            divider = number / i;
            foundIt=true;
        }
    }
    return divider;
}


bool IsItPrime (int number) {
    int i=1;
    bool isPrime=true;
    while (i<sqrt(number) && isPrime == true) {
        i++;
        if (number % i == 0) {
            isPrime=false;
        }
    }
    return isPrime;
}

The largest prime factor of 600851475143 is -127237759.