C ++在一行上测试CIN

Question

I've recently started teaching myself C++, and after having written a lot of user input code, it's made me wonder if there's a simpler way of handling it.

For example, the normal way of doing it would be like this:

#include <iostream>
using namespace std;

int inp;
int guess = 13;

void main(){
    cout << "Guess a number: ";
    cin >> inp;
    if (inp == guess)
        cout << endl << "Nice.";
}

But what I want to do is:

#include <iostream>
using namespace std;

int guess = 13;

void main(){
    cout << "Guess a number: ";
    if (cin == guess)
        cout << endl << "Even nicer.";
}

Is there a way to do this? Or this that just improper C++ standard?

Answer 1

In short: No, it's not possible to do as you want it.

You need to understand, that >> is actually a function call of

template<typename T>
std::istream& operator>>(std::istream& is, T& result);

and == is a function call to

template<typename T>
bool operator==(const std::istream&,const T& x);

Where the latter is used to check the stream state, and doesn't extract any user input.

To compare the input the result needs to be extracted from the std::istream in 1st place.

Answer 2

Well you can do it in one line but you don't really need to. But here are some examples anyway

//This will work for a char
#include <iostream>
#include <conio.h>

using namespace std;

int main()
{
    char test = 'a';
    if (getch()== test)
        cout<<"\n Works";
    return 0;
}

And if you really want

#include <iostream>
#include <conio.h>

using namespace std;

int main()
{
    int x =1;
    int y;
    for( cin >> y ; x == y ; )
    {
        cout<<"\n Works";
        break;
    }
    return 0;
}

Or as NathanOliver said you could simply do this

if( cin >> inp && inp == guess )

But really you want to keep it simple as this will confuse others as well as yourself after some time. You want to leave your code as easy as possible