How to keep taking 2 integers as input until program encounters a single integer?-CodePudding

I was given a question where the input will be like:

10 8
4 9
6 12
5 4
3
1

Here I don't know the number of lines that contains 2 integers. Those sets of 2 integers will be taken into an array. But when the program encounters "3", it will start taking input in another array.
I have tried this with
while(cin>>a>>b){ //some porcess with a and b }
but it doesn't work because it recognizes 3 and 1 as another set of two integers. Please help me to solve this problem.

CodePudding user response：

cin >> a >> b skips not only spaces, but any delimeter characters too ('\n', '\t', ' ').

Here you actually may want to read input line-by-line and then check if there are two integers or one. Consider use of std::getline for retrieving each line of text. Then you can use read string as std::istream (like in example in the link above) and read from it with counting, how many numbers you read totally.

CodePudding user response：

So think about your problem. Essentially it is, read one line at a time, and if it contains two numbers do one thing, but if it contains one number do something else.

But the code you have written reads numbers not lines. That is where the problem is.

Instead write your code to read only line at a time, analyse that line to see if it contains one or two numbers (or something else) and then proceed from there.

What you need is the ability to read a line of text into a string, and then read from that string into your numbers. To do that you use an istringstream. Something like this

#include <iostream>
#include <sstream>
#include <string>

int a, b;
string s;
getline(cin, s);       // read one line from standard input
istringstream line(s); // put that string to a stream we can read from
if (line >> a)         // try and read the first number from the stream
{
    // got the first number
    if (line >> b)     // try and read the second number from the stream
    {
        // got the second number
        ...
    }
    else
    {
        // only one number
        ...
    }
}
else
{
    // didn't get any numbers, some sort of error
    ...
}