当cin不是一个int时，C ++程序继续循环 [英] C++ program keeps looping when cin is not an int

问题描述

我使用C ++做一个简单的猜测数字游戏。
我的程序检查用户输入是否是一个整数。
但是当我输入例如abc时，程序保持说：输入一个数字！

 
 code> #include< iostream> 
 #include< cstdlib> 
 #include< ctime> 
 using namespace std; 
 
 int chances = 3; 
 void ask（）; 
 void checkAnswer（int ans）; 
 void defineNumber（）; 
 int correctAnswer; 
 
 void defineNumber（）{
 srand（time（0））; 
 correctAnswer = rand（）％11; 
} 
 
 void checkAnswer（int ans）{
 if（ans == correctAnswer）{
 cout< 答案是对的！\\\
< endl; 
 exit（0）; 
} else {
 if（chances> 0）{
 cout< 错误的答案，再试一次！\\\
< endl; 
 chances--; 
 ask（）; 
} else {
 cout<< 你输了！ << endl; 
 exit（0）; 
} 
} 
} 
 
 void ask（）{
 int input; 
 cout<< correctAnswer<< endl; 
 try {
 cin>>输入; 
 if（input> 11 || input< 0）{
 if（！cin）{
 cout< 输入数字！ << endl; // HERE LIES THE PROBLEM 
 cin.clear（）; // I TRIED THIS BID DID NOT WORK as WELL 
 ask（）; 
} else {
 cout<< 10岁以下你白痴！ << endl; 
 ask（）; 
} 
} else {
 checkAnswer（input）; 
} 
} catch（exception e）{
 cout<< 一个意料之外的问题发生了！ << endl; 
 ask（）; 
} 
} 
 
 int main（）{
 cout< 欢迎猜猜数字！ << endl; 
 cout<< 猜数10以下; 
 defineNumber（）; 
 ask（）; 
} 
  

提前感谢。

解决方案

尝试：

 试试{
 cin> ;输入; 
 if（cin.good（））{
 if（input> 11 || input< 0）{
 cout< 10岁以下你白痴！ << endl; 
 ask（）; 
} else {
 checkAnswer（input）; 
} 
 
} else {
 cout<< 输入数字！ << endl; 
 cin.clear（）; 
 cin.ignore（std :: numeric_limits< std :: streamsize> :: max（），'\\\
'）; 
 ask（）; 
} 
 
} catch（exception e）{
 cout<< 一个意料之外的问题发生了！ << endl; 
 ask（）; 
} 
  

并且不要忘记在开头使用： #include< climits>

cin.ignore（std :: numeric_limits< std :: streamsize> ; :: max（），'\\\
'）; 行将忽略一切，直到下一个int数字..因此它不会再循环..

I am making a simple guess the number game using C++. My program checks if the user input is an integer or not. But when I input for example "abc" the program keeps saying: "Input a number!" instead of saying it once and let the user input something again..

Code:

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int chances = 3;
void ask();
void checkAnswer(int ans);
void defineNumber();
int correctAnswer;

void defineNumber(){
    srand(time(0));
    correctAnswer = rand()%11;
}

void checkAnswer(int ans){
    if(ans == correctAnswer){
        cout << "The answer was right!\n" << endl;
        exit(0);
    }else{
        if(chances > 0){
            cout << "Wrong answer, try again!\n" << endl;
            chances--;
            ask();
        }else{
            cout << "You lost!" << endl;
            exit(0);
        }
    }
}

void ask(){
    int input;
    cout << correctAnswer << endl;
    try{
        cin >> input;
        if(input > 11 || input < 0){
            if(!cin){
                cout << "Input a number!" << endl; //HERE LIES THE PROBLEM
                cin.clear(); //I TRIED THIS BUT DIDN'T WORK AS WELL
                ask();
            }else{
                cout << "Under 10 you idiot!" << endl;
                ask();
            }
        }else{
            checkAnswer(input);
        }
    }catch(exception e){
        cout << "An unexpected error occurred!" << endl;
        ask();
    }
}

int main(){
    cout << "Welcome to guess the number!" << endl;
    cout << "Guess the number under 10: ";
    defineNumber();
    ask();
}

Thanks in advance.

解决方案

Try this:

try{
    cin >> input;
    if (cin.good()) {
      if(input > 11 || input < 0) {
        cout << "Under 10 you idiot!" << endl;
        ask();
      } else {
        checkAnswer(input);
      }

    } else {
      cout << "Input a number!" << endl;
      cin.clear();
      cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
      ask();
      }

}catch(exception e){
    cout << "An unexpected error occurred!" << endl;
    ask();
}

and don't forget to use this at the beginning: #include <climits>

The cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); line will ignore everything until the next int number.. Therefore it will not loop anymore..

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