JuniorTheoryCommon

What does the program print?

package main

import "fmt"

func main() {
    s := make([]int, 3)
    s = append(s, 7)
    fmt.Println(len(s), s)
}

4 [0 0 0 7]

Expecting 1 [7], as if make([]int, 3) only reserved room: it creates three elements set to zero, and append adds 7 after them.
Expecting append to fill the first zero: zeros are ordinary elements, so append always writes after the last one and the length grows to 4.

JuniorTheoryCommon

package main

import "fmt"

func main() {
    s := make([]int, 3)
    s = append(s, 7)
    fmt.Println(len(s), s)
}

4 [0 0 0 7]

Expecting 1 [7], as if make([]int, 3) only reserved room: it creates three elements set to zero, and append adds 7 after them.
Expecting append to fill the first zero: zeros are ordinary elements, so append always writes after the last one and the length grows to 4.