PROJECT EULER SOLUTION # 3

Solution to problem number 3 of Project Euler.

Question # 3

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

Solution # 3

/******************************************************************************/

#include<stdio.h>

#include<conio.h>

#include<math.h>

#include<time.h>

int isprime(long);

int main()

{

                long i;

                for(i=(long)sqrt(600851475143);i>=2;i--)

                {

                                if(isprime(i)&&(600851475143%i==0))

                                {

                                                printf("%ld\n",i);

                                                break;

                                }

                }

                printf("EXECUTION TIME = %f",clock()/(float)CLK_TCK);

                system("pause");

}

int isprime(long num)

{

                long i;

                for(i=2;i<=(long)sqrt(num);i++)

                                if(num%i==0)

                                                return 0;

                return 1;

}

/*******************************************************************************/