Question

Variable outside of the loop

int number = 0;
for(int i = 0; i < 10000; i++){
     number = 3 * i;
     printf("%d",number);
}

or Variable inside of the loop

for(int i = 0; i < 10000; i++){
     int number = 3 * i;
     printf("%d",number);
}

Which one is recommended and which one is better in performance?

Edit:

This is just an example to exhibit what I mean, All I wanna know is if defining a variable inside a loop and outside a loop means the same thing , or there’s a difference.

Answer 1

Time to learn something early: any optimization you could make on something like this will be irrelevant in the face of printf.

Printf will be very, very slow. You could quintuple the math and get no measurable speed decrease. It’s just the nature of printing to the terminal.

As for your edited question, there is no difference defining it in the loop or out. Imagine that

for (i = 0; i < 500; i++) {
  int a = i * 3;
}

is just the same as

int forloop::a; // This doesn't work, the idea is to show it just changes the scope
for (i = 0; i < 500; i++) {
  a = i * 3;
}

They will produce identical code, unless you start needing to use that variable outside of the loop it is defined in, because it is defined in the local scope of the loop. So…more like this:

int forloop::a;    // Still not valid code, just trying to show an explanation
namespace forloop {
for (i = 0; i < 500; i++) {
  a = i * 3;
}
} // namespace forloop

If this is unclear please let me know I’ll go into more detail or explain differently.