Why loops are needed in Go - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop in Go

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    for i := 1; i <= 3; i++ {
        fmt.Print(i, " ")
    }
}

A 1 2 3

B 1 2 3 4

C 0 1 2 3

D 123

💡 Hint

Look at the loop start and end values and what is printed inside the loop.

The loop starts at 1 and runs while i is less than or equal to 3, printing i and a space each time. So it prints '1 2 3 '.

🧠 Conceptual

intermediate

Why use loops instead of repeating code?

Why do programmers use loops instead of writing the same code many times?

A Loops are only used to confuse beginners.

B Loops make the program run slower but look nicer.

C Loops let us repeat actions easily without writing code again and again.

D Loops are used to stop the program from running.

💡 Hint

Think about what happens if you want to do the same thing many times.

Loops help repeat tasks without copying code multiple times, making programs shorter and easier to change.

❓ Predict Output

advanced

Output of nested loops in Go

What does this Go program print?

Go

package main
import "fmt"
func main() {
    for i := 1; i <= 2; i++ {
        for j := 1; j <= 2; j++ {
            fmt.Print(i*j, " ")
        }
    }
}

A 1 2 3 4

B 1 2 2 4

C 1 1 2 2

D 2 4 2 4

💡 Hint

Multiply i and j for each pair in the nested loops.

The outer loop runs i=1,2. For each i, inner loop runs j=1,2. The products are 1*1=1, 1*2=2, 2*1=2, 2*2=4 printed in order.

🔧 Debug

advanced

Identify the error in this Go loop

What error does this Go code cause?

Go

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

A Syntax error: missing semicolon after for statement

B Runtime error: index out of range

C No error, prints 0 1 2

D Syntax error: missing braces {} around loop body

💡 Hint

Check if the loop body is properly enclosed.

In Go, the for loop body must be inside braces {}. Without them, the code causes a syntax error.

🚀 Application

expert

Count how many times a loop runs

How many times does this loop run?

Go

package main
import "fmt"
func main() {
    count := 0
    for i := 10; i > 0; i -= 3 {
        count++
    }
    fmt.Println(count)
}

A 4

B 6

C 5

D 3

💡 Hint

Start at 10 and subtract 3 each time until i is no longer greater than 0.

The loop runs while i > 0: i=10,7,4,1 then stops when i= -2. So it runs 4 times.

Practice

1. Why do we use loops like for in Go programming?

easy

A. To stop the program from running

B. To store data permanently

C. To create new variables

D. To repeat a set of instructions multiple times without rewriting code

Solution

1. Step 1: Understand the purpose of loops

   Loops allow repeating actions multiple times without writing the same code again.

2. Step 2: Identify the correct use case

   Using loops saves time and makes code shorter and easier to manage.

3. Final Answer:

   To repeat a set of instructions multiple times without rewriting code -> Option D

4. Quick Check:

   Loops repeat actions = A [OK]

Hint: Loops repeat tasks to avoid rewriting code [OK]

Common Mistakes:

• Thinking loops store data
• Confusing loops with variable creation
• Believing loops stop program execution

2. Which of the following is the correct syntax for a basic for loop in Go?

easy

A. for i := 0; i < 5; i++ { fmt.Println(i) }

B. loop i from 0 to 5 { fmt.Println(i) }

C. while i < 5 { fmt.Println(i) }

D. repeat 5 times { fmt.Println(i) }

Solution

1. Step 1: Recall Go loop syntax

   Go uses for with initialization, condition, and post statement separated by semicolons.

2. Step 2: Match syntax to options

   for i := 0; i < 5; i++ { fmt.Println(i) } matches Go's for loop syntax exactly.

3. Final Answer:

   for i := 0; i < 5; i++ { fmt.Println(i) } -> Option A

4. Quick Check:

   Go uses for with semicolons = C [OK]

Hint: Go loops use for with semicolons, not while or loop [OK]

Common Mistakes:

• Using while instead of for
• Using loop keyword which Go doesn't have
• Missing semicolons in for loop

3. What will be the output of this Go code?

for i := 1; i <= 3; i++ {
    fmt.Print(i, " ")
}

medium

A. 1 2 3

B. 0 1 2 3

C. 1 2 3 4

D. 3 2 1

Solution

1. Step 1: Analyze loop range

   The loop starts at i=1 and runs while i is less than or equal to 3, incrementing by 1 each time.

2. Step 2: Trace output for each iteration

   It prints 1, then 2, then 3, each followed by a space.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Loop prints 1 to 3 = D [OK]

Hint: Check loop start, end, and increments carefully [OK]

Common Mistakes:

• Starting loop from 0 instead of 1
• Including extra numbers beyond 3
• Printing in reverse order

4. Identify the error in this Go loop code:

for i := 0; i < 5 i++ {
    fmt.Println(i)
}

medium

A. Incorrect variable declaration

B. Using wrong loop keyword

C. Missing semicolon between condition and increment

D. Missing braces around loop body

Solution

1. Step 1: Check for syntax errors in for loop

   Go requires semicolons separating initialization, condition, and post statements in for loops.

2. Step 2: Locate missing semicolon

   The code misses a semicolon between i < 5 and i++.

3. Final Answer:

   Missing semicolon between condition and increment -> Option C

4. Quick Check:

   For loop parts need semicolons = A [OK]

Hint: Remember semicolons separate for loop parts [OK]

Common Mistakes:

• Omitting semicolons in for loop header
• Using while instead of for
• Forgetting braces for loop body

5. You want to print all even numbers from 2 to 10 using a loop in Go. Which code snippet correctly does this?

hard

A. for i := 2; i < 10; i += 2 { fmt.Println(i) }

B. for i := 1; i <= 10; i++ { if i%2 == 0 { fmt.Println(i) } }

C. for i := 2; i < 10; i++ { if i%2 == 0 { fmt.Println(i) } }

D. for i := 2; i <= 10; i++ { fmt.Println(i*2) }

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 inclusive.

2. Step 2: Check each option

   for i := 2; i < 10; i += 2 { fmt.Println(i) } prints 2,4,6,8 missing 10.
   for i := 1; i <= 10; i++ { if i%2 == 0 { fmt.Println(i) } } loops 1 to 10 and prints only if number is even.
   for i := 2; i < 10; i++ { if i%2 == 0 { fmt.Println(i) } } loops 2 to 9, missing 10.
   for i := 2; i <= 10; i++ { fmt.Println(i*2) } prints multiples of i*2, which gives 4,6,8,... not correct.

3. Step 3: Identify the correct option

   for i := 1; i <= 10; i++ { if i%2 == 0 { fmt.Println(i) } } correctly prints all even numbers from 2 to 10 inclusive.

4. Final Answer:

   for i := 1; i <= 10; i++ { if i%2 == 0 { fmt.Println(i) } } -> Option B

5. Quick Check:

   Check condition inside loop for even numbers = B [OK]

Hint: Use if inside loop to filter even numbers [OK]

Common Mistakes:

• Forgetting to include 10 in range
• Incrementing by wrong step
• Printing wrong multiples