Looping with for

The while pattern we just learned — counting from zero to a limit — is so common that AHA! Lang provides a more concise form: for with a number range.

Basic Form

for i in 0..5 {
    print(i);
}

Output:

0
1
2
3
4

Structure:

for <variable> in <start>..<end> {
    ...code to repeat...
}

• The variable (e.g. i) automatically holds the current round's value.
• The range 0..5 means: start from 0, up to but not including 5 (5 is not included). This is called an exclusive end.
• No need to declare or increment a counter manually — the compiler handles it all.

How Many Times Does the Loop Run?

for i in 0..3 { print(i); }   // 0, 1, 2       → 3 times
for i in 1..4 { print(i); }   // 1, 2, 3       → 3 times
for i in 0..1 { print(i); }   // 0             → 1 time
for i in 0..0 { print(i); }   // (nothing)     → 0 times

The formula: the range a..b runs b - a rounds.

Summing with for

Remember the 1..100 exercise with while? The for version is much shorter:

let total = 0;

for i in 1..101 {
    total = total + i;
}

print(total); // 5050

break and continue in for

Same as while:

// break: stop early
let total = 0;
for i in 0..100 {
    if i == 5 {
        break;
    }
    total = total + i;
}
print(total); // 0 + 1 + 2 + 3 + 4 = 10

// continue: skip one round
let jumlah_ganjil = 0;
for i in 0..10 {
    if i % 2 == 0 {
        continue;
    }
    jumlah_ganjil = jumlah_ganjil + i;
}
print(jumlah_ganjil); // 1 + 3 + 5 + 7 + 9 = 25

Using the Loop Variable

The range variable can be used in any calculation:

// multiplication table of 7
for i 1..11 {
    print(7 * i);
}
// 7, 14, 21, ..., 70

while or for?

Both have break/continue, so you can start with whichever feels most natural.

Exercises

1. Print all even numbers from 0 to 20 using for and i % 2.
2. Compute the product 1 * 2 * 3 * ... * 10 (factorial of 10) — start from hasil = 1.
3. Print the squares from 1 to 10 (i * i).
4. Combine for and if: count how many numbers from 1 to 50 are divisible by 5.

On to Functions