C输入验证

Question

有人能帮我完成输入验证功能吗。我正在验证整数输入。问题是当用户输入多个整数my cin时。fail（）对每个整数运行，导致我的错误显示多次。让我告诉你我的意思

这是我的代码：

#include <iostream>
//#include "Uni.hpp"
#include <string>

using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::getline;

int main()
{

bool repeat;
int choice; 
repeat = false;

//Give user options     
cout << "Enter 1:   Print building information" << endl;
cout << "Enter 2:   Print people information" << endl;
cout << "Enter 3:   Assign work to a Student or instructor." << endl;
cout << "Enter 4:   Exit program." << endl;
cin >> choice;



//First check for correct data type integers only in this case 
while (cin.fail())
{
    cout << "Enter only an integer please. Try again." << std::endl;
    cin.clear();
    cin.ignore();
    cin >> choice;
}

//run program until user exits
while (choice != 4)
{
    if (choice == 1)
    {
        cout << "Print building info" << endl;
    }

    if (choice == 2)
    {
        cout << "Print people info" << endl;
    }

    if (choice == 3)
    {
        cout << "Assign work" << endl;
    }

    if (choice > 4)
    {
        cout << "Not a valid choice. Choose " << endl;
    }

    cout << endl;
    cout << endl;
    //give options again 
    cout << "Enter 1:   Print building information" << endl;
    cout << "Enter 2:   Print people information" << endl;
    cout << "Enter 3:   Assign work to a Student or instructor." << endl;
    cout << "Enter 4:   Exit program." << endl;
    cin >> choice;

    //data type validation
    while (cin.fail())
    {
        cout << "Enter only an integer please." << endl;
        cin.clear();
        cin.ignore();
        cin >> choice;
    }

因此，如果用户要输入“jjj”；我的“请只输入整数”显示三次。我只想让它显示一次。我不知道怎么做。有什么想法吗？

Answer 1

首先测试cin.fail，打印一次消息，然后处理并清除循环中的字符。这将解释例如，人们键入“bbb”，这将触发循环中的三次运行，但它只会给你一次消息：

    if (cin.fail())
    {
        cout << "Enter only an integer please." << endl;
    }
    //data type validation
    while (cin.fail())
    {
        cin.clear();
        cin.ignore();
        cin >> choice;
    }

您还可以将指令/输入验证代码移动到while循环的顶部，然后您不需要在while循环之外重复它