Loops and functions

1. What is this?

A loop repeats a block. for (int i = 1; i <= 5; i++) runs with i = 1..5. A function is a reusable block: int doubleIt(int n) takes an int and returns an int. Declare it before main (or prototype it) so main can call it.

2. Why do we use it?

Games loop over frames; engines call the same function millions of times. Write once, run fast.

3. Syntax breakdown

• int doubleIt(int n) { return n * 2; }

  Function taking int n, returning n*2.

• for (int i = 1; i <= 3; i++) {

  Loop i from 1 while <= 3.

•   std::cout << doubleIt(i) << std::endl;

  Calls the function each pass and prints the result.

5. Common mistakes

• Calling a function before it is declared — define it above main.
• Forgetting the return type (int) before the function name.
• Off-by-one loop bounds.

Practice task

Make tripleIt (n * 3) and print tripleIt(i) for i = 1..5.

Press Run to see output.

Mini quiz

3 questions. Answer, then check.

1. 1. Where must a function be relative to its use?

   Declared before useAfter main alwaysIn another file only

2. 2. What does int before a function name mean?

   It returns an intIt takes no inputIt loops

3. 3. How many passes for i=1; i<=5?

   546