从cin读取int编号，直到按ESC C ++

Question

I am interested to find a solution for the following problem:

I have to read int numbers form CIN until the user presses ESC and compute the average of the positive and even integers.

My problem is i am not quite sure how correctly write the stopping condition.

Here's what i've tried so far(not working properly)

#include<iostream>
#include<math.h>

using namespace std;

void main()
{
    int c, sum=0, i=0;
cout<<"Insert characters: ";
while(cin>>c)
{
    i++;
    if((int)c>=0&&(int)c%2==0){
        sum+=(int)c;
    }
}
cout<<"Average: "<<(float)sum/i<<endl;
system("pause");
}

Answer 1

You can try this

while((ch = cin.get()) != 27)
{
  i++;
  if((int)ch>=0&&(int)ch%2==0
  {
    sum+=(int)ch;
  }
}

This should loop until the esc key is pressed

Answer 2

The escape character is neither a digit nor a space. Thus, if the program gets passed the character in the stream, you can just read integers and the stream will automatically fail when an espace characters is entered (just concentrating on the input aspect of the question):

#include<iostream>

int main()
{
    int c = 0;
    while (std::cin >> c) {
        std::cout << "c=" << c << '\n';
    }
}

Whether the escape characters is forwarded to the stream by the operating system is, however, a different question. For example, on UNIXes the escape character will be forwarded but only when the input is given to the program which, by default, is when a line is entered. If the program shouldn't wait for the return key, the operating system needs to get told to not wait for the return key.

The question seems to be for Windows but I don't know enough about Windows to determine how to change the terminal settings there (see below for something which may still work, though). On UNIXes, you'd clear the ICANON flag in the terminal settings using tcgetattr() and tcsetattr() . For example, you could use this:

#include <iostream>
#include <termios.h>

int main()
{
    termios values;
    tcgetattr(0, &values);
    values.c_lflag &= ~ICANON;
    tcsetattr(0, TCSANOW, &values);

    int c = 0;
    while (std::cin >> c) {
        std::cout << "c=" << c << '\n';
    }
}

I think there is getch() on Windows which get you one character without waiting. This, hopefully, also includes the escape character. If that's the case you could just create a simple stream buffer around getch() and use that instead:

#include <iostream>
#include <streambuf>
#include <whatever-declares-getch>

struct getchbuf
    : std::streambuf {
    static int const end = <getch()-error-value-goes-here>;
    char buffer;
    int underflow() {
        int result(traits_type::eof());
        if (this->gptr() == this->egptr() && (result = getch()) != end) {
            buffer = traits_type::to_char_type(result);
            this->setg(&buffer, &buffer, &buffer + 1);
        }
        return result;
    }
};

int main()
{
    getchbuf sbuf;
    std::istream in(&sbuf);

    int c = 0;
    while (in >> c) {
        std::cout << "c=" << c << '\n';
    }
}

You need to patch up the above code to include whatever declares getch() (I think it is <conio.h> but I don't know) and to specify getch() 's error indicator.