c ++终止while循环，以'|'读取数字

Question

I am currently working through a book on C++ and I am stumped by a very simple problem.

Trying to write a program that takes in two integers, outputs them, and repeats.

What is causing me problems is that the program is supposed to be terminated when '|' is entered to the console.

I've tried this:

(inside of while loop)

char c;
int a, b;
cin >> c;
a = c;
if (c == '|')
    break
a = c - 48;
cin >> b;
b = c;
if (c == '|')
    break;
b = c - 48;
.....

Obviously this only works for a small range of numeric inputs. Is there a better approach that will give me the ability to enter in multidigit numbers and detect if '|' has been entered? Apologies if this seems basic, statically typed languages are not my forte.

Answer 1

The obvious way would to use a loop, and check the conversion by testing the stream's conversion to bool after reading (or at least, attempting to read):

int i;
while (std::cin >> i)         // Try to read a number
    std::cout << i << "\t";   // if successful, print it out

if (std::cin.peek == '|')     // check why reading a number failed.
    // end of input detected
else
    // invalid input detected

Answer 2

I think, you should change your terminating condition. In that case, if your terminating condition is any non number input (char, string), you can get your expected result (works for integer range of numeric inputs).

You can try like this...

...
if (!(cin >> a))
{
    break;
}

if (!(cin >> b))
{
    break;
}
...
//Uncomment the below two lines if you want to take more input
//cin.clear();
//cin.ignore(std::numeric_limits<int>::max(), '\n');

For your understanding

if ( !(cin >> vaiable) ) is true, it means that

a) the entered value does not fit the variable

b) the variable will not be affected

c) the stream is still broken

d) the entered value is still in the buffer and will be used for the next "cin >> variable" statement.

---

If you want to process further input, do the following:

a) repair the stream via cin.clear();

b) clear the buffer with cin.ignore(std::numeric_limits::max(),'\\n');