learngo/11-if/questions/3-if.md

What does "control flow" mean?

1. Changing the top-to-bottom execution of a program
2. Changing the left-to-right execution of a program
3. Deciding which statements are executed CORRECT

1, 2: You can't change that.

3: That's right. Control flow allows us to decide which parts of a program is to be run depending on condition values such as true or false.

How can you simplify the condition expression of this if statement?

if (mood == "perfect") {
    // this code is not important
}

1. if {mood == "perfect"}
2. if [mood == "perfect"]
3. if mood = "perfect"
4. if mood == "perfect" CORRECT

1, 2: That's a syntax error. Try again.

3: = is the assignment operator. It cannot be used as a condition.

4: That's right. In Go, you don't need to use the parentheses.

The following code doesn't work. How you can fix it?

package main

import "fmt"

func main() {
    // this program prints "cool"
    // when the mood is "happy"

    mood := "happy"

    if "happy" {
        fmt.Println("cool")
    }
}

1. Just wrap the "happy" inside parentheses.
2. You need to compare mood with "happy". Like this: if mood == "happy" { ... } CORRECT
3. Just directly use mood instead of happy. Like this: if mood { ... }
4. This should work! This is a tricky question.

1: That won't change anything. Go adds the parentheses automatically behind the scenes for every if statement.

2: Yep. In Go, condition expressions always yield a bool value. Using a comparison operator will yield a bool value. So, it will work.

4: No, it's not :)

How can you simplify the following code? You only need to change the condition expression, but how?

package main

import "fmt"

func main() {
    happy := true

    if happy == true {
        fmt.Println("cool!")
    }
}

1. happy != false
2. !happy == false
3. happy CORRECT
4. !happy == true

1, 2: Right! But you can do it better.

3: Perfect! You don't need to compare the value to true. happy is already true, so it'll print "cool!".

4: That won't print anything. !happy yields false.

How can you simplify the following code? You only need to change the condition expression, but how?

package main

import "fmt"

func main() {
    happy := false

    if happy == !true {
        fmt.Println("why not?")
    }
}

1. Easy! Like this: happy != true
2. !happy CORRECT
3. happy == false
4. !happy == false

1, 3: Right! But you can do it better.

2: Perfect! You don't need to compare the value to false or to !true (which is false). !happy already returns true, because it's false at the beginning.

4: That won't print anything. happy will be true.

This code contains an error. How to fix it?

package main

import "fmt"

func main() {
    happy := false

    if happy {
        fmt.Println("cool!")
    } else if !happy {
        fmt.Println("why not?")
    } else {
        fmt.Println("why not?")
    } else {
        fmt.Println("why not?")
    }
}

1. Remove one of the else branches. CORRECT
2. Move the else if as the last branch.
3. It repeats "why not?" several times.
4. Remove the else if branch.

1: Right. There can be only one else branch.

2: If there's an else branch, you can't move else if branch as the last branch.

3, 4: So? :) That's not the cause of the problem.

What's the problem with the following code?

package main

import "fmt"

func main() {
    happy := true
    energic := happy

    if happy {
        fmt.Println("cool!")
    } else if !happy {
        fmt.Println("why not?")
    } else if energic {
        fmt.Println("working out?")
    }
}

1. It declares the energic variable unnecessarily.
2. You can't use more than one else if branch.
3. It will never run the last else if branch. CORRECT
4. There's no else branch.

2: Well, actually you can.

3: Right. happy can only be either true or false. That means, it will always execute the first two branches, but it will never execute the else if branch.

4: It doesn't have to be. Else branch is optional.

How can you simplify the following code?

package main

import "fmt"

func main() {
    happy := false

    if happy {
        fmt.Println("cool!")
    } else if happy != true {
        fmt.Println("why not?")
    } else {
        fmt.Println("why not?")
    }
}

1. Change else if's condition to: !happy.
2. Move the else branch before else if.
3. Remove the else branch.
4. Remove the else if branch. CORRECT

1, 3: Close! But, you can do it even better.

2: You can't: else branch should be the last branch.

4: Cool. That's not necessary because else branch already handless "unhappy" situation. It's simpler because it doesn't have a condition.