Loops: Conditionals

In the previous lesson, we used an infinite for loop with a break statement to control when to exit. Go provides a cleaner way to handle this common pattern: adding a condition directly to the for loop.

The Conditional Loop

Instead of an infinite loop with break, you can specify a condition that's checked before each iteration. The loop continues as long as the condition is true.

counter := 0
for counter < 5 {
    fmt.Println(counter)
    counter++
}
// Prints: 0, 1, 2, 3, 4

This is similar to a while loop in other programming languages, but Go uses for for all looping needs.

How it Works

The loop checks the condition before each iteration:

1. Check if the condition is true
2. If true, execute the loop body
3. Repeat from step 1
4. If false, exit the loop

power := 1
for power < 100 {
    fmt.Println("Power level:", power)
    power = power * 2
}
// Prints: 1, 2, 4, 8, 16, 32, 64

Once power reaches 128, the condition power < 100 becomes false, and the loop exits.

Conditional vs Infinite with Break

Compare these two approaches that accomplish the same thing:

// Using infinite loop with break
count := 0
for {
    if count >= 3 {
        break
    }
    fmt.Println(count)
    count++
}

// Using conditional loop - cleaner!
count := 0
for count < 3 {
    fmt.Println(count)
    count++
}

The conditional loop is more readable and conventional when you have a simple condition to check.

When to Use Each Style

// Use conditional loops when you have a clear stopping condition
attempts := 0
for attempts < 5 {
    fmt.Println("Attempt:", attempts)
    attempts++
}

// Use infinite loops with break for more complex exit conditions
for {
    userInput := getUserInput()
    if userInput == "quit" || errorOccurred {
        break
    }
    processInput(userInput)
}

Assignment

For this challenge, create a function called countdown that accepts a parameter n (an int).

The function should:

• Use a for loop with a condition (not an infinite loop)
• Start at n and count down to 1
• Print each number as you count down
• Stop when you reach 0 (don't print 0)

Important: If n is 0 or negative, the loop should not run at all.

The function signature is:

func countDown(n int) {
    // Your code here
}

For example, calling countDown(5) should print:

5
4
3
2
1