Conditions and loops have to be written, not just read. Five tasks, from easy to harder. Write a function, run it on the examples, then compare with the solution.

1 (easy) — grade. Turn a score into a grade: 90+ → "A", 80+ → "B", 70+ → "C", else "F". Use a valueless switch (switch { case ... }).

grade(95) → "A"      grade(83) → "B"      grade(60) → "F"

func grade(score int) string {
    switch {
    case score >= 90:
        return "A"
    case score >= 80:
        return "B"
    case score >= 70:
        return "C"
    default:
        return "F"
    }
}

2 (easy) — sign. Return "positive", "negative" or "zero" (plain if).

sign(5) → "positive"      sign(-2) → "negative"      sign(0) → "zero"

func sign(n int) string {
    if n > 0 {
        return "positive"
    }
    if n < 0 {
        return "negative"
    }
    return "zero"
}

3 (medium) — sumRange. Add the integers from lo to hi inclusive (a classic for).

sumRange(1, 5) → 15

func sumRange(lo, hi int) int {
    total := 0
    for i := lo; i <= hi; i++ {
        total += i
    }
    return total
}

4 (medium) — fizzbuzz. From 1 to n: "Fizz" if divisible by 3, "Buzz" if by 5, "FizzBuzz" if by both, else the number itself. Return []string.

fizzbuzz(5) → [1 2 Fizz 4 Buzz]

func fizzbuzz(n int) []string {
    out := []string{}
    for i := 1; i <= n; i++ {
        switch {
        case i%15 == 0:
            out = append(out, "FizzBuzz")
        case i%3 == 0:
            out = append(out, "Fizz")
        case i%5 == 0:
            out = append(out, "Buzz")
        default:
            out = append(out, fmt.Sprint(i))
        }
    }
    return out
}

5 (harder) — digitSum. Add up a number's digits. Hint: n % 10 is the last digit, n /= 10 removes it.

digitSum(1234) → 10      digitSum(-99) → 18

func digitSum(n int) int {
    if n < 0 {
        n = -n
    }
    sum := 0
    for n > 0 {
        sum += n % 10
        n /= 10
    }
    return sum
}

Tip. Call each function from main (fmt.Println(grade(95))) and check it against the examples. These pure functions (no input, no state) are exactly what we'll test automatically with go test in lesson 13.