Thread: Stuck in a vector size loop

Hey guys.

Is there any reason why I have created an infinite loop here if input?
I have stated I only wish 5 names to be entered and I have set the loop
condition to the size of the vector using the function.

And I push_back() the name each iteration to add it to the vector, but
when I run the program it will not stop asking for input even when it goes
past the 4th input ( which is the fifth ).

I am sure it is such a tiny mistake - if anyone can point me in the right
direction I would greatly appriciate it.

Code:

#include <iostream>
#include <string>
#include <vector>

// main function - begin program execution 
int main ( void ) {
	const int SIZE = 5;
	std::string name = "";

	std::vector < std::string > myVec( SIZE, "" );

	for ( unsigned int counter = 0; counter < myVec.size(); counter++ ) {
		std::cout << "Enter name " << counter << ": ";
		std::getline( std::cin, name );

		myVec.push_back( name );
	}

	std::cout << "\n\nYou entered these five names:\n\n";

	for ( unsigned int counter = 0; counter < myVec.size(); counter++ ) {
		std::cout << myVec[ counter ] << std::endl;
	}

	std::cin.get(); // freeze console window
	std::cin.ignore();

	return 0; // indicate sucessful termination
}

push_back grows the vector. You leave the first 5 items empty and keep adding to the end.

Simply loop 5 times and don't size the vector to begin with.

At this line, you create a vector of 5 strings:

Code:

std::vector < std::string > myVec( SIZE, "" );

Here, you keep looping as long as the counter is less than the size of the vector:

Code:

for ( unsigned int counter = 0; counter < myVec.size(); counter++ ) {

Now, you increase the size of the vector by 1:

Code:

myVec.push_back( name );

Therefore, when you next compare the counter with the size of the vector, you compare 1 with 6. On the next iteration, you will compare 2 with 7. In general, the comparison is always x < x + 5, which is always true, hence the loop is an infinite loop.

One solution is to simply not use push_back, e.g.,

Code:

myVec[counter] = name;

Another solution is to use push_back, but create an empty vector instead, changing the loop condition to counter < SIZE.

Thank you so much for the advice guys

Very imformative - I will take your advice on board.