基于变量的for循环的方向

Question

I have a couple of biggish for loops which I would like to separate into functions to reduce code duplication.

The only difference between them is the first line of the loop.

One is:

for (int j = 50; j < average_diff; j++) {

The other is:

for (int j = upper_limit; j > lower_limit; j--) {

I have an integer, tb which indicates which one I'd like to use (it has a value of 1 or 2 respectively).

I'm wondering how I might best accomplish this. Is this a good use case for macros?

Answer 1

No, doesn't sound like a good case for macros at all.

The best (most C++-ish) thing would probably be to use a range , and pass that to the function.

Answer 2

Don't wrap the for , just wrap the contents in a function:

for (int j = 50; j < average_diff; j++) {
   process(j);
}

for (int j = upper_limit; j > lower_limit; j--) {
   process(j);
}

Answer 3

If your variable is, like you say, 1 for one direction and 2 for another, you can use the ternary operator ?: :

for (int i = (dir == 1 ? 0 : 20);
     dir == 1 ? i < upper_limit :
                i > lower_limit;
     i += (dir == 1 ? 1 : -1))
{
    ...
}

However, it might be more readable if you just use a simple if statement:

if (dir == 1)
{
    for (int i = 0; i < upper_limit; i++)
    {
    }
}
else
{
    for (int i = 20; i > lower_limit; i--)
    {
    }
}

If you go with the last, then I suggest you put the code inside the loop in a separate function that you call, so you don't have any duplicate code.