If & Switch Statements

Control flow statements let your program make decisions. In this lesson, you'll learn how to use if statements for simple conditions and switch statements for multiple choices, making your Go programs dynamic and responsive.

If Statements

The if statement executes code when a condition is true. Unlike many languages, Go doesn't require parentheses around the condition:

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If-Else and Else If

// If-else
if age >= 18 {
    fmt.Println("Adult")
} else {
    fmt.Println("Minor")
}

// Else if chain
if score >= 90 {
    fmt.Println("Grade: A")
} else if score >= 80 {
    fmt.Println("Grade: B")
} else if score >= 70 {
    fmt.Println("Grade: C")
} else {
    fmt.Println("Grade: F")
}

If with Short Statement

Go allows you to execute a short statement before the condition. This is useful for limiting variable scope:

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Common Pattern: Error Checking

// Common Go pattern
if err := doSomething(); err != nil {
    fmt.Println("Error:", err)
    return
}

// err is not accessible here

// Another example
if value, ok := myMap["key"]; ok {
    fmt.Println("Found:", value)
} else {
    fmt.Println("Not found")
}

Switch Statements

Switch statements provide a cleaner way to write multiple if-else conditions:

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Switch Without Condition

A switch without a condition is the same as switch true, making it a cleaner if-else chain:

hour := time.Now().Hour()

switch {
case hour < 12:
    fmt.Println("Good morning!")
case hour < 18:
    fmt.Println("Good afternoon!")
default:
    fmt.Println("Good evening!")
}

Multiple Values in Case

day := "Saturday"

switch day {
case "Saturday", "Sunday":
    fmt.Println("It's the weekend!")
case "Monday":
    fmt.Println("Start of the week")
default:
    fmt.Println("It's a weekday")
}

Fallthrough

If you need C-style fallthrough behavior, use the fallthrough keyword:

switch num := 2; num {
case 1:
    fmt.Println("One")
case 2:
    fmt.Println("Two")
    fallthrough  // Continues to next case
case 3:
    fmt.Println("Three")
}
// Output: Two
//         Three

Type Switch

Type switches allow you to compare types instead of values. This is useful when working with interfaces:

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switch v := i.(type) {
case int:
    // v is an int
case string:
    // v is a string
default:
    // v has the same type as i
}

If vs Switch: When to Use Which?

Common Mistakes

// ❌ Wrong - won't compile
x := 5
if x {  // Error: non-bool used as if condition
    fmt.Println("x is truthy")
}

// ✅ Correct - explicit comparison
if x != 0 {
    fmt.Println("x is not zero")
}

// ❌ Wrong - syntax error
if x > 5
    fmt.Println("Greater")

// ✅ Correct - braces required
if x > 5 {
    fmt.Println("Greater")
}

// ❌ Wrong expectation (from C/Java)
switch x {
case 1:
    fmt.Println("One")
case 2:
    fmt.Println("Two")
}
// Only prints "One" if x is 1, not "One" and "Two"

// ✅ Correct - Go doesn't fall through by default
// This is actually the desired behavior!

// ❌ Wrong - syntax error
if x > 5
{
    fmt.Println("Greater")
}

// ✅ Correct - brace on same line
if x > 5 {
    fmt.Println("Greater")
}

Exercise: Grade Calculator

package main

import "fmt"

func main() {
    score := 85
    var grade string
    
    // Determine letter grade
    if score >= 90 {
        grade = "A"
    } else if score >= 80 {
        grade = "B"
    } else if score >= 70 {
        grade = "C"
    } else if score >= 60 {
        grade = "D"
    } else {
        grade = "F"
    }
    
    fmt.Printf("Score: %d, Grade: %s\n", score, grade)
    
    // Provide feedback based on grade
    switch grade {
    case "A":
        fmt.Println("Excellent work!")
    case "B":
        fmt.Println("Good job!")
    case "C":
        fmt.Println("Satisfactory")
    case "D":
        fmt.Println("Needs improvement")
    case "F":
        fmt.Println("Please see instructor")
    }
    
    // Bonus: Check if passing
    switch {
    case score >= 60:
        fmt.Println("Status: Passing")
    default:
        fmt.Println("Status: Failing")
    }
}

Summary

What's Next?

Now that you can make decisions in your code, it's time to learn about Loops & Range. In the next lesson, you'll discover how to repeat code execution and iterate over collections.