C++ 程序在将 int 与 cin 但不是字符串一起使用时工作

Question

I wrote this simple program to more or less "warm up" in using C++ and when asking for a string input, the program stops working as intended.

Here it is asking for an int, which works as intended:

#include <iostream>

using namespace std;

int main() {
    cout << "enter something\n";
    int usertypestuff;
    cin >> usertypestuff;
    cout << usertypestuff << " is a number.";
}

Output is as follows:

Windows PowerShell
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Try the new cross-platform PowerShell https://aka.ms/pscore6

PS C:\Users\fortm\Documents\CPPPrac> cd "c:\Users\fortm\Documents\CPPPrac\MainPrac\" ; if ($?) { g++ Main.cpp -o Main } ; if ($?) { .\Main }
enter something
12.5
12 is a number.
PS C:\Users\fortm\Documents\CPPPrac\MainPrac> 

However, when changing code to use a string instead, the program skips over "enter something" and the cin lines and jumps to a new line (for commands and etc.) instead.

Non-working code:

#include <iostream>
#include <string>

using namespace std;

int main() {
    cout << "enter something\n";
    string usertypestuff;
    cin >> usertypestuff;
    cout << usertypestuff << " is a number.";
}

Output log:

Windows PowerShell
Copyright (C) Microsoft Corporation. All rights reserved.

Try the new cross-platform PowerShell https://aka.ms/pscore6

PS C:\Users\fortm\Documents\CPPPrac> cd "c:\Users\fortm\Documents\CPPPrac\MainPrac\" ; if ($?) { g++ Main.cpp -o Main } ; if ($?) { .\Main }
PS C:\Users\fortm\Documents\CPPPrac\MainPrac> 12
12
PS C:\Users\fortm\Documents\CPPPrac\MainPrac> hu
hu : The term 'hu' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1
+ hu
+ ~~
    + CategoryInfo          : ObjectNotFound: (hu:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

PS C:\Users\fortm\Documents\CPPPrac\MainPrac> 

I've tried compiling with both MinGW and CygWin to no avail and am running the program with coderunner (run in terminal is checked) in Visual Studio code.

Answer 1

It worked fine when i did it..

Code:

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

int main() {
    cout << "enter something\n";
    string usertypestuff;
    cin >> usertypestuff;
    cout << usertypestuff << " is a number.";
    return 0;
}

Output:

enter something
25
25 is a number.

Answer 2

You can use std::to_string() function to convert usertypestuff to string,

string str = to_string(usertypestuff);

Answer 3

cin >> usertypestuff;

The std::operator>>(std::istream&, std::string&) method reads from the stream until it finds a space, and then returns. Then the rest of the program runs. Your code is fine, but I suspect that while running the program in a terminal, you're entering an input that has a space in the middle. The program reads up to the space, then finishes running correctly, and then exits. After that, the terminal reads the rest of the input as the next program to run. But since your input wasn't a valid command, the terminal displays a CommandNotFoundException .