c++ - 检查计算是否会导致溢出c++

Question

我在 collat​​z() 中添加了 elseif 语句来检查工作编号 * 3 + 1 是否会超过 INT_MAX，但在运行程序时，一些不应该超过 INT_MAX 的数字被报告为这样做。我可能不需要强制转换 INT_MAX，但我不确定。

#include <iostream>
#include <cstdlib>
#include <climits>

using namespace std;

void collatz( int startingnumber ) {

    int count = 0;

    int originalnumber = startingnumber;

    int workingnumber = startingnumber;

    while( workingnumber >= 1 ) {

        if( workingnumber == 1 ) {

            cout << originalnumber << " takes " << count << " steps" << endl;

            count = 0;

            break;
        }

        if( workingnumber % 2 == 0 ) {

            workingnumber /= 2;

            //optional
            //cout << originalnumber << " is at " << workingnumber << endl;

            count++;
        }
        else if( ( ( long int ) workingnumber * 3 ) + 1 > ( long int ) INT_MAX ) {

            cout << originalnumber << " will cause a buffer overflow" << endl;

            break;
        }        
        else {

            workingnumber = ( 3 * workingnumber ) + 1;

            //optional
            //cout << originalnumber << " is at " << workingnumber << endl;

            count++;
        }
    }
}

int main( int argc, char* argv[] ) {

    int increment = 2;

    if( argc > 1 ) {

        if( atoi( argv[1] ) != 0 ) {

            increment = atoi( argv[1] );
        }
    }

    while( increment <= INT_MAX ) {

        collatz( increment );

        increment++;
    }

    return 0;
}

Answer 1

当您需要对大数进行运算时，最好使用任意精度算术库，例如 GNU MPFR .

这样，您就不必担心整数溢出。