c++ - 如果用户输入无效则循环

Question

我想创建一个程序，当用户输入我没有定义的内容时，程序会再次提示他。

我用 if 语句完成了它，但它只循环了 1 次并且不再执行。我尝试了循环，但只要输入为假，它就会打破条件并拒绝所有输入。在 C++ 中。

非常感谢任何帮助。

#include <iostream>
#include <string>
using namespace std;


void xD(){string x;
   do{cout << "Retry\n";
    cin >> x;}while(true);}
//declaring a function to make the shop
void shop(){
    string x;
    float coins = 500;
    float bow_cost = 200;

 cout  << "welcome to the shop\n";

 cout  << "Bow(bow)costs 150 coins.\n";

        cin >> x;
 // if u chose bow you get this and get to choose again
        if (x == "bow"){
        cout << "you bought the bow.\n you now have " <<coins - bow_cost << " coins." << endl; cin >> x;}

/*now the problem that whenever I excute the code and type something other than bow it gives me the cin only once more and then fails even if I type bow in the 2nd attempt*/ 



//in my desperate 5k attempt, I tried creating a function for it.. no use.
//i want it o keep prompting me for input till i type "bow" and the other block excutes. but it never happens. 
     else{xD();}

}
int main(){
    string name;
    string i;

  cout << "if you wish to visit the shop type \"shop\"\n";


    cin >> i;


       if(i == "shop"){shop();}
       else{cin >> i;}
        return 0;
    }  

Answer 1

问题出在这个循环 block 中的条件

void xD(){
  string x;
  do{
    cout << "Retry\n";
    cin >> x;
  }while(true);
}

无论输入如何，while(true) 条件都会使其永远循环。要解决此问题，您可以更改条件:

void xD(){
  string x;
  do{
    cout << "Retry\n";
    cin >> x;
  }while(x!="bow");
 cout << "you bought the bow. and some other messages"<<endl;
}

那应该行得通。但是，这对我来说仍然太复杂了。这可以简化为以下代码段:

void shop(){
  string x;
  float coins = 500;
  float bow_cost = 200;

  cout  << "welcome to the shop\n";

  cout  << "Bow(bow)costs 150 coins.\n";

  cin >> x;
  while (x!="bow"){
    cout << "Retry\n";
    cin>>x;
  }
  cout << "you bought the bow.\n you now have " <<coins - bow_cost << " coins." << endl; cin >> x;

}