“整数常量对于‘long’来说太大了；类型”当找到最大素因数时

Question

我正在致力于解决 Euler 项目 3：

Description: The prime factors of 13195 are 5, 7, 13 and 29.
             What is the largest prime factor of the number 600851475143 ?

这是我生成答案的代码。但是我需要一个整数类型来保存600851475143。当我在 Mac 上的 GCC 上编译它时，我得到：

integer constant is too large for ‘long’ type". 

我预计 long long 可以轻松保存这个数字。我也尝试将其设为未签名。为什么我的代码不能保存那么小的数字，我该怎么做才能使它工作？

#include <iostream>
#include <vector>

using namespace std;

static bool IsPrimeFactor(int numToTest,int testNum,vector<int> factors)
{
    if(numToTest%testNum==0) // is it a factor?
    {
        // see if it is a prime factor
        for(unsigned int i=0; i < factors.size(); i++)
        {
            if(testNum%factors[i]==0)  // see if this factor
            {                          //is divisble by one we have already

                return false;
            }
        }

        return true;
    }
    return false;
}

int main() {
    unsigned long long numToTest=600851475143;
    unsigned int testNum=2;  // 0 and 1 are assumed
    vector<int> factors;   

    while(testNum<numToTest)   // don't go higher than the max num
    {
        if(IsPrimeFactor(numToTest,testNum,factors)) // is it a factor?
        {
            factors.push_back(testNum); // got through prime factors 
        }                                   // and none divided it

        testNum++;
    }

    for(unsigned int i=0; i < factors.size(); i++)
    {
        cout << "factor " <<factors[i] << endl;
    }

    cout<<"Highest factor: " << factors[factors.size()-1]<<endl;

    return 0;
}

Answer 1

检查这个问题。你必须像这样指定你的文字：

600851475143LL

Answer 2

正如@Space_C0wb0y所说，您需要为文字指定一个后缀。

另外，您的 IsPrimeFactor 函数将会遇到问题 - 参数是整数，但正如您已经发现的那样，整数甚至长整型都不足以存储您的数字会反复经过...