Question

此代码存在一些问题：

void selectOption(){
    int choice; cin >> choice;
    string name, surname;
    switch(choice){
        case 1:
            showStudents();
            break;
        case 2:
            cout <<"Name: "; cin >> name;
            cout <<"Surname: "; cin >> surname;
            addStudent(name,surname);
            break;
        case 3:
            break;
        default:
            cout <<"DOES NOT SUPPORT" << endl;
            break;
    }
}

int main(){
    while(true){
        selectOption();
    }
}

问题是，每当我输入字符串时，程序都会进入default的情况，而不是让我输入选择。

第二个问题是，该程序只能在1、2和3上运行。如果我写5，则什么也不会发生（甚至不会进入default情况）。

Answer 1

在尝试执行任何操作之前，您需要检查输入的值是否为整数，否则可能会收到一些非常令人讨厌的未定义行为。有many个简单的方法可以做到这一点，我个人的偏爱是使用std::all_of中的algorithm来检查输入中的每个字符是否都是数字。当然，这需要您像这样将输入作为std::string

#include <iostream>
#include <string>
#include <algorithm>

void showStudents() {
  // Show students  
}
void addStudent(std::string name, std::string surname) {
  // Add student
}

void selectOption(){
  int choice = 0;
  std::string in = ""; 
  std::cout << "Choice: " << std::flush;
  std::cin >> in;
  if (std::all_of(in.begin(), in.end(), ::isdigit)) {
    choice = std::stoi(in);
  }
  std::string name, surname;
  switch(choice){
    case 1:
      showStudents();
      break;
    case 2:
      std::cout <<"Name: "; 
      std::cin >> name;
      std::cout <<"Surname: "; 
      std::cin >> surname;
      addStudent(name,surname);
      break;
    case 3:
      break;
    default:
      std::cout << "DOES NOT SUPPORT" << std::endl;
      return;
  }
}

int main() {
  while(true) {
    selectOption();
  }
}

这将产生您期望的行为-输入任何字符串，它将进入默认大小写，输入1，2或3并执行该大小写。输出示例：

Choice: string
DOES NOT SUPPORT
Choice: 1
Choice: 2
Name: Name
Surname: Surname
Choice: 3
Choice: 4
DOES NOT SUPPORT
Choice: 5
DOES NOT SUPPORT
Choice: t
DOES NOT SUPPORT
Choice:

Answer 2

这似乎可以正常工作。有什么问题吗？

#include <iostream>
#include <string>

using namespace std;


void selectOption()
{
    int choice;
    string name, surname;

    cin >> choice;
    switch(choice)
    {
        case 1:
            cout << "showStudents()" << endl;
            break;
        case 2:
            cout <<"Name: "; cin >> name;
            cout <<"Surname: "; cin >> surname;
            cout << "addStudent(" << name << "," << surname << ")" << endl;
            break;
        case 3:
            break;
        default:
            cout <<"DOES NOT SUPPORT" << endl;
            break;
    }
}

int main(){
    while(true){
        selectOption();
    }
}

输出：

> 1 showStudents() 
> 2 
> Name: Rufus 
> Surname: VonWoodson
> addStudent(Rufus,VonWoodson) 
> 3 
> 4 
> DOES NOT SUPPORT 
> 5 
> DOES NOT SUPPORT 
> 6
> DOES NOT SUPPORT 
> ^C 
> Command terminated
> 
> Interrupt: Press ENTER or type command to continue

Answer 3

在开关中，您想测试整数的条件，如果您输入字符串作为变量选择，它将进入默认情况（希望我理解了这个问题）

Switch在while循环中不断进入默认情况

3 个答案: