What is the largest prime factor of the number 600851475143? - c

Question

I want to know that what is the error in my code.
int main () {
long long int number, large_factor=0, i=2;
printf ("Enter a number : ");
scanf ("%ld", &number);
while (number!=1) {
if (number%i==0) {
while (number%i==0) {
printf ("%ld\t", i);
number/=i;
}
large_factor=i;
}
i++;
}
printf ("\n\nThe largest prime factor is : %ld\n\n", large_factor);
return 0;
}
This code is running fine for smaller numbers but why it is failing for the large numbers?

Answer 1

Your format specifier everywhere is for long int you should use "%lld".

Answer 2

When I fix the format specifiers it runs fine for 600851475143 giving the largest prime factor 6857.
There must be something else going on. Assuming your compiler is compliant long long int should (at minimum) be a 64-bit integer and easily large enough to accommodate that value.
Try
printf("long long int max : %lld\n",LLONG_MAX);
Having added #include <limits.h> at the top.
It should produce a value no less than 9223372036854775807 and probably that exact number.
Here:
#include <limits.h>
#include <stdio.h>
int main () {
printf("long long int max : %lld\n",LLONG_MAX);
long long int large_factor=0, i=2;
long long int number=600851475143;
while (number!=1) {
if (number%i==0) {
while (number%i==0) {
printf ("%lld\t", i);
number/=i;
}
large_factor=i;
}
i++;
}
printf ("\n\nThe largest prime factor is : %lld\n\n", large_factor);
return 0;
}