String Input error when using stringstream and if-else statement - c++

Question

I am trying to write a part of a large code where a string of 2 numbers is inputted by the user and each number is parsed from the string to do simple addition (just wanted to test the parsing for now).
I do the parsing using stringstream which seems to work but using this code to compute multiple cases is not working. Please see code and output below;
#include <iostream>
#include <sstream>
int main()
{
int t;
std::cout << "Enter the number of test cases: ";
std::cin >> t;
std::cout << std::endl;
if (t > 10 || t < 1)
{
std::cout << "Invalid number of test cases!" << std::endl;
return 0;
}
else
{
for (int x = 0; x < t; x++)
{
std::stringstream numbers;
int num_1;
int num_2;
std::cout << "Enter the two numbers (separated by a space): " << std::endl;
std::string input;
getline (std::cin, input);
numbers << input;
numbers >> num_1 >> num_2;
std::cout << num_1 << std::endl;
std::cout << num_2 << std::endl;
std::cout << num_1 + num_2 << std::endl;
}
}
return 0;
}
Code Output
CODE OUTPUT
Enter the two numbers (separated by a space):
0
-13120
-13120
Enter the two numbers (separated by a space):
1 3
1
3
4
Enter the two numbers (separated by a space):
4 5
4
5
9
Enter the two numbers (separated by a space):
6 7
6
7
13
Why is the first case not taking inputs?

Answer 1

Change code early in main to this:
std::cout << "Enter the number of test cases: ";
std::cin >> t; std::cin.ignore();
When you cin>>t, it reads in the number you give it and then stops. Your next input is a getline, which reads to the next end of line...which is the one you typed after the number of test cases. So you're using an empty line for your first input.
cin.ignore() tells it to skip that empty line and go on to whatever you type next.

Answer 2

First, using a value from cin without checking the stream state is almost as bad as using an uninitialized value. Take advantage of the streams explicit bool operator. Second, you are over complicating the code, why would you read in a string of numbers, only too parse them as numbers?
You can simply do this: with an arbitrary number of objects:
cin >> arg1 >> arg2 >> arg3 >> ...
I've modifed your code with these issues in mind:
#include <iostream>
#include <sstream>
int main()
{
int t;
std::cout << "Enter the number of test cases:\n";
if (std::cin >> t) { // succeeded in getting an int
if (t > 10 || t < 1) { // failed in getting a valid number of test cases
std::cout << "Invalid number of test cases!" << std::endl;
return 1; // return value of 0 is reserved for a successful run, returning zero after an error doesn't make sense
}
else { // succeeded in getting a valid number of test cases
for (int x = 0; x < t; x++) {
int num_1;
int num_2;
std::cout << "Enter the two numbers (separated by a space): " << std::endl;
// why use a stringstream here when you can get the same affect by just retrieving
// two integers from cin
if (std::cin >> num_1 >> num_2) { // again always check for valid input
std::cout << num_1 << std::endl;
std::cout << num_2 << std::endl;
std::cout << num_1 + num_2 << std::endl;
}
else { // failed in getting two int's
//...
// handle error
}
}
}
}
else {
//...
// handle error
}
return 0;
}