For loop basics in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop with continue

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    for i := 0; i < 5; i++ {
        if i == 2 {
            continue
        }
        fmt.Print(i)
    }
}

A 01234

B 0134

C 0123

D 1234

💡 Hint

Remember that continue skips the current loop iteration.

The loop prints numbers from 0 to 4 but skips printing 2 because of continue.

❓ Predict Output

intermediate

For loop with range over slice

What will this Go program print?

Go

package main
import "fmt"
func main() {
    nums := []int{10, 20, 30}
    sum := 0
    for _, v := range nums {
        sum += v
    }
    fmt.Println(sum)
}

A 60

B 0

C 10

D 30

💡 Hint

The loop adds all numbers in the slice.

The sum of 10 + 20 + 30 is 60, so the program prints 60.

🔧 Debug

advanced

Identify the error in this for loop

What error will this Go code produce when compiled?

Go

package main
func main() {
    for i := 0; i < 5; i++ {
        println(i)
    }
}

A No error, prints 0 1 2 3 4

B Runtime error: index out of range

C Syntax error: missing braces for for loop body

D Syntax error: unexpected semicolon

💡 Hint

Check the syntax rules for for loops in Go.

Go requires braces {} around the loop body; missing them causes a syntax error.

❓ Predict Output

advanced

Nested for loops output

What does this Go program print?

Go

package main
import "fmt"
func main() {
    for i := 1; i <= 2; i++ {
        for j := 1; j <= 3; j++ {
            fmt.Print(i * j)
        }
    }
}

A 123246

B 123456

C 112233

D 136236

💡 Hint

Multiply i and j for each iteration and print without spaces.

First outer loop i=1: prints 1*1=1,1*2=2,1*3=3 → 123; second i=2: 2*1=2,2*2=4,2*3=6 → 246; combined: 123246.

❓ Predict Output

expert

For loop with break and label

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
Outer:
    for i := 1; i <= 3; i++ {
        for j := 1; j <= 3; j++ {
            if i*j >= 4 {
                break Outer
            }
            fmt.Print(i, j, " ")
        }
    }
}

A 11 12 21

B 1 1 1 2 2 1

C 11 12 13

D 11 12 13 21

💡 Hint

The break with label stops both loops when i*j >= 4.

Prints for (1,1):11 , (1,2):12 , (1,3):13 , (2,1):21 then at i=2 j=2 (4>=4) breaks Outer without printing more.

Practice

1. What does a for loop do in Go programming?

easy

A. Stops the program immediately

B. Imports a package

C. Defines a new variable

D. Repeats a block of code while a condition is true

Solution

1. Step 1: Understand the purpose of a for loop

   A for loop is used to repeat code multiple times based on a condition.

2. Step 2: Identify the correct description

   Only Repeats a block of code while a condition is true correctly describes repeating code while a condition is true.

3. Final Answer:

   Repeats a block of code while a condition is true -> Option D

4. Quick Check:

   For loop = Repeat code [OK]

Hint: For loops repeat code while condition is true [OK]

Common Mistakes:

• Thinking for loop stops program
• Confusing for loop with variable declaration
• Mixing for loop with import statements

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

easy

A. for i := 0; i < 5; i++ { }

B. for (i = 0; i < 5; i++) { }

C. for i in range(5) { }

D. loop i from 0 to 5 { }

Solution

1. Step 1: Recall Go for loop syntax

   Go uses for init; condition; post { } syntax without parentheses.

2. Step 2: Compare options

   for i := 0; i < 5; i++ { } matches Go syntax exactly. Options B, C, and D use other languages or invalid syntax.

3. Final Answer:

   for i := 0; i < 5; i++ { } -> Option A

4. Quick Check:

   Go for loop = for init; condition; post [OK]

Hint: Go for loops use semicolons, no parentheses [OK]

Common Mistakes:

• Using parentheses like in C or Java
• Using Python-style for-in loops
• Writing 'loop' instead of 'for'

3. What is 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. Syntax error

Solution

1. Step 1: Analyze loop range and output

   The loop starts at i=1 and runs while i <= 3, so i takes values 1, 2, 3.

2. Step 2: Understand print output

   Each iteration prints i followed by a space, so output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Loop prints 1 to 3 with spaces [OK]

Hint: Check loop start, end, and print inside loop [OK]

Common Mistakes:

• Starting loop at 0 instead of 1
• Including extra number beyond 3
• Confusing print with println

4. Identify the error in this Go for loop:

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

medium

A. Using := instead of = for i

B. Missing semicolon between condition and post statement

C. Using parentheses around for loop

D. Missing curly braces

Solution

1. Step 1: Check for loop syntax parts

   Go requires semicolons between init, condition, and post parts 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 post statement -> Option B

4. Quick Check:

   For loop parts separated by semicolons [OK]

Hint: Check semicolons between for loop parts [OK]

Common Mistakes:

• Omitting semicolons in for loop header
• Confusing := with = in loop variable
• Forgetting curly braces

5. How can you use a for loop in Go to sum all even numbers from 2 to 10 inclusive?

hard

A. for i := 2; i < 10; i += 2 { sum += i }

B. for i := 0; i <= 10; i += 2 { sum += i }

C. for i := 1; i <= 10; i++ { if i%2 == 0 { sum += i } }

D. for i := 2; i < 10; i++ { sum += i*2 }

Solution

1. Step 1: Understand the goal

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

2. Step 2: Analyze each option

   for i := 2; i < 10; i += 2 { sum += i } increments by 2 starting at 2, but i < 10 so sums only 2+4+6+8 (misses 10).
   for i := 1; i <= 10; i++ { if i%2 == 0 { sum += i } } loops from 1 to 10, checks if number is even, then adds it. This is correct and clear.
   for i := 2; i < 10; i++ { sum += i*2 } incorrectly multiplies i by 2 and sums, which is wrong.
   for i := 0; i <= 10; i += 2 { sum += i } starts at 0, which includes 0 in sum, not desired.

3. Final Answer:

   for i := 1; i <= 10; i++ { if i%2 == 0 { sum += i } } -> Option C

4. Quick Check:

   Check even with modulo inside loop [OK]

Hint: Use modulo to check even numbers inside loop [OK]

Common Mistakes:

• Starting loop at 0 including unwanted numbers
• Multiplying instead of checking evenness
• Forgetting to check condition inside loop