Variadic Sum

A variadic parameter accepts any number of arguments, including none. It is written ...T and has to be the last parameter:

func Sum(nums ...int) int {
	total := 0
	for _, n := range nums {
		total += n
	}
	return total
}

Sum()           // 0
Sum(1, 2, 3)    // 6

Inside the function nums is an ordinary []int. With no arguments it is nil, which has length zero and ranges zero times, so the empty case usually needs no code at all.

To pass a slice you already have, spread it with ...:

values := []int{1, 2, 3}
Sum(values...)      // 6
Sum(values)         // does not compile: []int is not an int

The two forms are not the same underneath. Sum(1, 2, 3) builds a fresh slice; Sum(values...) passes values itself, so the parameter shares the caller's backing array. A variadic function that writes to its parameter writes to the caller's slice.

When you need "at least one", put a required parameter in front of the variadic: func Largest(first int, rest ...int) int cannot be called with nothing, and the compiler enforces it rather than a runtime check.

Task

Fill in the six functions in main.go.

1. Sum(nums ...int) int adds its arguments; no arguments is 0.
2. Largest(first int, rest ...int) int returns the biggest value.
3. SumAll(groups ...[]int) int adds every number in every group, by calling Sum with each group spread.
4. Average(nums ...int) (float64, bool) returns the mean, and false when there are no arguments.
5. Describe(format string, args ...any) string forwards to fmt.Sprintf.
6. SumEvens(nums ...int) int adds only the even arguments, leaving the caller's slice untouched.

Hints

• Sum() needs no if. The parameter is nil, range over nil runs zero times, and the total stays 0.
• SumAll is a variadic of slices. The outer call spreads groups in; Sum(group...) spreads each group back out.
• Average divides by len(nums), which is why it has to check for zero first: integer or not, dividing by zero here is a panic.
• float64(Sum(nums...) / len(nums)) is already wrong - it does the integer division and then converts the wrong answer. Convert both operands first.
• Describe must end in args..., not args. Passing the slice itself makes it one argument of type []any, and %s has %d then prints %!s(...) noise instead of the values.
• The last test calls SumEvens(nums...) and checks nums afterwards. As long as you only read the parameter you are fine; a solution that sorts or compacts it in place will fail there and not in the sum.