Golang tricky output based interview questions

Sankalp polSankalp pol
8 min read

I've curated a list of output based questions for Golang interviews.

If you find any question difficult, Go Tour(https://go.dev/tour/welcome/1) is your best help. It will take atmost two days to cover all the slides.

After solving all, you will realize Golang has its own quirks, just like Javascript.

For answers, checkout: https://github.com/SankalpSTG/go-guide/blob/main/interview-questions/output-based/answers/README.md

Q1. What will be the output for the following code

package main

import "fmt"

func main() {
    funcs := []func(){}
    for i := 0; i < 3; i++ {
        funcs = append(funcs, func() { fmt.Println(i) })
    }
    for _, f := range funcs {
        f()
    }
}

Q2. What will be the output for the following code

package main

import "fmt"

func main() {
    s := []int{1, 2, 3}
    t := s[:2]
    t = append(t, 99)
    fmt.Println("s:", s)
    fmt.Println("t:", t)
}

Q3. What will be the output for the following code

package main

import "fmt"

func f() (x int) {
    defer func() {
        x++
    }()
    return 1
}

func main() {
    fmt.Println(f())
}

Q4. What will be the output for the following code

package main

import "fmt"

type T struct{}

func (t *T) String() string {
    return "I'm T"
}

func main() {
    var t *T = nil
    var i fmt.Stringer = t
    fmt.Println(i == nil)
    fmt.Println(i)
}

Q5. What will be the output for the following code

package main

import "fmt"

func main() {
    ch1 := make(chan int)
    ch2 := make(chan int)

    go func() {
        ch1 <- 1
    }()

    select {
    case x := <-ch1:
        fmt.Println("Received", x)
    case y := <-ch2:
        fmt.Println("Received", y)
    }
}

Q6. What will be the output for the following code

package main

import "fmt"

func main() {
    x := 5
    {
        x := x
        fmt.Println(x)
    }
}

Q7. What will be the output for the following code

package main

import "fmt"

func main() {
    defer fmt.Println("deferred")
    panic("something went wrong")
    fmt.Println("after panic")
}

Q8. What will be the output for the following code

package main

import "fmt"

func main() {
    s := []int{1, 2, 3}
    t := s
    s = append(s[:1], s[2:]...)
    fmt.Println("s:", s)
    fmt.Println("t:", t)
}

Q9. What will be the output for the following code

package main

import "fmt"

type MyStruct struct{}

func (m *MyStruct) Error() string {
    return "error from MyStruct"
}

func main() {
    var m *MyStruct = nil
    var err error = m
    fmt.Println(err == nil)
    fmt.Println(err)
}

Q10. What will be the output for the following code

package main

import (
    "fmt"
    "time"
)

func main() {
    ch := make(chan int)

    select {
    case v := <-ch:
        fmt.Println("Received", v)
    default:
        fmt.Println("No value received")
    }

    time.Sleep(time.Second)
}

Q11. What will be the output for the following code

package main

import "fmt"

func main() {
    m := map[string]int{
        "a": 1,
        "b": 2,
        "c": 3,
    }

    for k, v := range m {
        fmt.Println(k, v)
    }
}

Q12. What will be the output for the following code

package main

import "fmt"

func main() {
    nums := []int{1, 2, 3}
    var ptrs []*int

    for _, n := range nums {
        ptrs = append(ptrs, &n)
    }

    for _, p := range ptrs {
        fmt.Println(*p)
    }
}

Q13. What will be the output for the following code

package main

import "fmt"

func main() {
    s := "hello"
    b := []byte(s)
    b[0] = 'H'
    fmt.Println(s)
    fmt.Println(string(b))
}

Q14. What will be the output for the following code

package main

import (
    "fmt"
    "time"
)

func main() {
    for i := 0; i < 3; i++ {
        go func() {
            fmt.Println(i)
        }()
    }
    time.Sleep(time.Second)
}

Q15. What will be the output for the following code

package main

import "fmt"

func main() {
    var i interface{} = 10
    s := i.(string)
    fmt.Println(s)
}

Q16. What will be the output for the following code

package main

import "fmt"

func main() {
    m := map[string]int{"a": 1, "b": 2}
    var ptrs []*int

    for _, v := range m {
        ptrs = append(ptrs, &v)
    }

    for _, p := range ptrs {
        fmt.Println(*p)
    }
}

Q17. What will be the output for the following code

package main

import "fmt"

func main() {
    a := []int{1, 2, 3, 4}
    b := a[:2]
    c := a[2:]
    b = append(b, 99)
    fmt.Println("a:", a)
    fmt.Println("b:", b)
    fmt.Println("c:", c)
}

Q18. What will be the output for the following code

package main

import "fmt"

func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered:", r)
        } else {
            fmt.Println("No panic occurred")
        }
    }()
    fmt.Println("Doing fine")
}

Q19. What will be the output for the following code

package main

import "fmt"

func main() {
    const x = 10
    {
        var x = 20
        fmt.Println(x)
    }
    fmt.Println(x)
}

Q20. What will be the output for the following code

package main

import "fmt"

type Person struct {
    name string
}

func main() {
    p1 := Person{name: "Alice"}
    p2 := p1
    p2.name = "Bob"

    fmt.Println(p1.name)
    fmt.Println(p2.name)
}

Q21. What will be the output for the following code

package main

import "fmt"

func main() {
    var a []int
    b := []int{}

    fmt.Println(a == nil)
    fmt.Println(b == nil)
}

Q22. What will be the output for the following code

package main

import "fmt"

func main() {
    for i := 0; i < 3; fmt.Println(i) {
        i++
    }
}

Q23. What will be the output for the following code

package main

import "fmt"

func modifyArr(a [3]int) {
    a[0] = 100
}

func modifySlice(s []int) {
    s[0] = 100
}

func main() {
    arr := [3]int{1, 2, 3}
    slice := []int{1, 2, 3}

    modifyArr(arr)
    modifySlice(slice)

    fmt.Println(arr)
    fmt.Println(slice)
}

Q24. What will be the output for the following code

package main

import "fmt"

func main() {
    res := make([][]int, 0)
    row := []int{}

    for i := 0; i < 3; i++ {
        row = append(row, i)
        res = append(res, row)
    }

    fmt.Println(res)
}

Q25. What will be the output for the following code

package main

import "fmt"

func main() {
    x := 2
    switch x {
    case 1:
        fmt.Println("One")
        fallthrough
    case 2:
        fmt.Println("Two")
        fallthrough
    case 3:
        fmt.Println("Three")
    default:
        fmt.Println("Default")
    }
}

Q26. What will be the output for the following code

package main

import "fmt"

func main() {
    var nums []int

    for _, v := range nums {
        fmt.Println(v)
    }

    fmt.Println("done")
}

Q27. What will be the output for the following code

package main

import "fmt"

func main() {
    ch := make(chan int)
    ch <- 10
    fmt.Println("done")
}

Q28. What will be the output for the following code

package main

import "fmt"

func main() {
    s := make([]int, 0, 2)
    capBefore := cap(s)

    s = append(s, 1)
    s = append(s, 2)
    capAfter := cap(s)

    s = append(s, 3)
    capFinal := cap(s)

    fmt.Println(capBefore, capAfter, capFinal)
}

Q29. What will be the output for the following code

package main

import "fmt"

func main() {
    var i interface{} = nil
    fmt.Println(i == nil)

    var p *int = nil
    i = p
    fmt.Println(i == nil)
}

Q30. What will be the output for the following code

package main

import "fmt"

type A struct{}

func (a A) Foo() {
    fmt.Println("A Foo")
}

type B struct {
    A
}

func main() {
    b := B{}
    b.Foo()
}

Q31. What will be the output for the following code

package main

import "fmt"

func main() {
    var s1 []int
    s2 := []int{}

    fmt.Println(len(s1), cap(s1), s1 == nil)
    fmt.Println(len(s2), cap(s2), s2 == nil)
}

Q32. What will be the output for the following code

package main

import "fmt"

func main() {
    x := 5
    defer fmt.Println(x)
    x = 10
}

Q33. What will be the output for the following code

package main

import "fmt"

func main() {
    var m1 map[string]int
    m2 := make(map[string]int)

    fmt.Println(m1 == nil)
    fmt.Println(m2 == nil)

    m2["key"] = 1
    // m1["key"] = 1  // Uncommenting this will cause what?
}

Q34. What will be the output for the following code

package main

import "fmt"

func main() {
    s := []int{1, 2, 3, 4, 5}
    s1 := s[:3]
    s2 := s[3:]

    s1 = append(s1, 10)
    s2[0] = 20

    fmt.Println(s)
    fmt.Println(s1)
    fmt.Println(s2)
}

Q35. What will be the output for the following code

package main

import "fmt"

func main() {
    var i interface{} = (*int)(nil)

    v, ok := i.(*int)
    fmt.Println(v, ok)
}

Q36. What will be the output for the following code

package main

import "fmt"

func main() {
    m := map[int]string{
        1: "one",
        2: "two",
        3: "three",
    }

    for k := range m {
        fmt.Print(k, " ")
    }
}

Q37. What will be the output for the following code

package main

import "fmt"

func main() {
    ch := make(chan int, 3)
    ch <- 1
    ch <- 2
    ch <- 3
    close(ch)

    for v := range ch {
        fmt.Print(v, " ")
    }
}

Q38. What will be the output for the following code

package main

import (
    "encoding/json"
    "fmt"
)

type Base struct {
    ID int `json:"id"`
}

type User struct {
    Base
    Name string `json:"name"`
}

func main() {
    data := []byte(`{"id":10, "name":"Alice"}`)
    var u User
    json.Unmarshal(data, &u)
    fmt.Println(u.ID, u.Name)
}

Q39. What will be the output for the following code

package main

import "fmt"

const (
    a = iota
    b
    c = 5
    d
    e = iota
)

func main() {
    fmt.Println(a, b, c, d, e)
}

Q40. What will be the output for the following code

package main

import "fmt"

func main() {
    var err error
    fmt.Println(err == nil)

    err = (*struct{})(nil)
    fmt.Println(err == nil)
}

Q41. What will be the output for the following code

package main

import "fmt"

func main() {
    s := []int{1, 2, 3, 4, 5}
    s1 := s[:3]
    s2 := s1[:4]

    fmt.Println(s2)
}
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golanginterview questionsGo Languageoutput based

Written by

Sankalp pol
Sankalp pol