Question

Alright, I wanna know why this code is working, I just realized that I have two variables with the same name within the same scope.

I’m using g++ (gcc 4.4).

for(int k = 0 ; k < n ; k++)
    {
        while(true)
        {
            i = Tools::randomInt(0, n);
            bool exists = false;

            for(int k = 0 ; k < p_new_solution_size ; k++)
                if( i == p_new_solution[k] )
                {
                    exists = true;
                    break;
                }
            if(!exists)
                break;
        }

        p_new_solution[p_new_solution_size] = i;
        p_new_solution_size++;
    }

Answer 1

Alright, I wanna know why this code is working, I just realized that I have two variables with the same name within the same scope.

You seem confused about scopes. They’re not “within the same” scope… the for loop’s k has it’s own nested/inner scope. More importantly, to see why the language allows it, consider:

#define DO_SOMETHING \
    do { for (int i = 1; i <= 2; ++i) std::cout << i << '\n'; } while (false)

void f()
{
    for (int i = 1; i <= 10; ++i)
        DO_SOMETHING();
}

Here, the text substituted by the macro “DO_SOMETHING” gets evaluated in the same scope as i. If you’re writing DO_SOMETHING, you may need its expansion to store something in a variable, and settle on the identifier i – obviously you have no way of knowing if it’ll already exist in the calling context. You could try to pick something more obscure, but you’d have people using such convoluted variable names that their code maintainability suffered, and regardless sooner or later there would be a clash. So, the language just lets the inner scopes introduce variables with the same name: the innermost match is used until its scope exits.

Even when you’re not dealing with macros, it’s a pain to have to stop and think about whether some outer scope is already using the same name. If you know you just want a quick operation you can pop it an indepedent (nested) scope without considering that larger context (as long as you don’t have code in there that actually wants to use the outer-scope variable: if you do then you can sometimes specify it explicitly (if it’s scoped by namespaces and classes, but if it’s in a function body you do end up needing to change your own loop variable’s name (or create a reference or something to it before introducing your same-named variable)).