Loop execution flow in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested loops with continue

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    for i := 1; i <= 3; i++ {
        for j := 1; j <= 3; j++ {
            if j == 2 {
                continue
            }
            fmt.Printf("%d%d ", i, j)
        }
    }
}

A 11 12 13 21 22 23 31 32 33

B 11 13 22 23 31 33

C 12 13 22 23 32 33

D 11 13 21 23 31 33

💡 Hint

Remember that continue skips the rest of the current loop iteration.

The inner loop skips printing when j == 2. So for each i, it prints j=1 and j=3 only.

❓ Predict Output

intermediate

Loop with break inside if condition

What will this Go program print?

Go

package main
import "fmt"
func main() {
    for i := 0; i < 5; i++ {
        if i == 3 {
            break
        }
        fmt.Print(i)
    }
}

A 0123

B 012

C 01234

D 123

💡 Hint

Break exits the loop immediately when the condition is met.

The loop prints numbers starting from 0. When i == 3, it breaks out of the loop, so it prints 0,1,2 only.

❓ Predict Output

advanced

Output of loop with labeled break

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 > 3 {
                break Outer
            }
            fmt.Printf("%d%d ", i, j)
        }
    }
}

A 11 12 21

B 11 12 21 22 23

C 11 12 21 22

D 11 12 13 21 22 23 31 32 33

💡 Hint

The labeled break exits the outer loop when the condition is true.

When i*j > 3, the program breaks out of the outer loop completely. The last printed pair is 22 before breaking.

❓ Predict Output

advanced

Loop with post statement modifying loop variable

What will this Go program print?

Go

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

A 024

B 01234

C 135

D 0134

💡 Hint

Notice that i++ is called inside the loop body and also in the for statement.

The loop increments i twice each iteration: once in the body and once in the for statement. So it prints 0, 2, 4.

🧠 Conceptual

expert

Number of iterations in complex loop

Consider this Go code snippet. How many times will the inner loop's body execute?

for i := 1; i <= 4; i++ {
    for j := i; j <= 4; j++ {
        // loop body
    }
}

A 10

B 16

C 6

D 4

💡 Hint

Count the number of pairs (i,j) where j >= i and both go up to 4.

For i=1, j=1..4 (4 times); i=2, j=2..4 (3 times); i=3, j=3..4 (2 times); i=4, j=4..4 (1 time). Total = 4+3+2+1 = 10.

Practice

1. What is the main purpose of a for loop in Go?

easy

A. To handle errors

B. To define a new variable

C. To repeat a block of code while a condition is true

D. To declare a function

Solution

1. Step 1: Understand the role of loops

   Loops are used to repeat actions multiple times based on a condition.

2. Step 2: Identify the purpose of for in Go

   In Go, the for loop is the only loop and repeats code while a condition holds true.

3. Final Answer:

   To repeat a block of code while a condition is true -> Option C

4. Quick Check:

   Loop = repeat code [OK]

Hint: Loops repeat code while condition true [OK]

Common Mistakes:

• Confusing loops with variable declarations
• Thinking loops handle errors
• Mixing loops with function declarations

2. Which of the following is the correct syntax for a basic for loop in Go that runs 3 times?

easy

A. for i := 0; i < 3; i++

B. for (i = 0; i < 3; i++) { }

C. for i = 0; i < 3; i++ { }

D. for i := 0; i < 3; i++ { }

Solution

1. Step 1: Check Go loop syntax

   Go requires initialization with :=, condition, and post statement inside parentheses without extra parentheses around the whole for.

2. Step 2: Validate each option

   for i := 0; i < 3; i++ { } uses correct syntax: for i := 0; i < 3; i++ { }. Options B and C have wrong parentheses or missing :=. for i := 0; i < 3; i++ misses braces.

3. Final Answer:

   for i := 0; i < 3; i++ { } -> Option D

4. Quick Check:

   Correct Go for loop syntax = for i := 0; i < 3; i++ { } [OK]

Hint: Use := for init, semicolons, braces for loop [OK]

Common Mistakes:

• Using parentheses like C/Java
• Missing := for variable declaration
• Omitting braces {}

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

for i := 1; i <= 3; i++ {
    if i == 2 {
        continue
    }
    fmt.Print(i)
}

medium

A. 13

B. 12

C. 123

D. 23

Solution

1. Step 1: Understand the loop and continue

   The loop runs i from 1 to 3. When i equals 2, continue skips printing.

2. Step 2: Trace output for each i

   i=1 prints '1', i=2 skips print, i=3 prints '3'. Output is '13'.

3. Final Answer:

   13 -> Option A

4. Quick Check:

   Continue skips i=2 print = 13 [OK]

Hint: Continue skips current iteration print [OK]

Common Mistakes:

• Assuming continue prints the skipped value
• Confusing continue with break
• Ignoring loop condition

4. Identify the error in this Go loop code:

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

medium

A. Missing braces {} around loop body

B. Incorrect loop condition

C. Variable i not declared

D. Using println instead of Println

Solution

1. Step 1: Check Go loop syntax rules

   Go requires braces {} to define the loop body even if it is one statement.

2. Step 2: Identify missing braces

   The code lacks braces around fmt.Println(i), causing a syntax error.

3. Final Answer:

   Missing braces {} around loop body -> Option A

4. Quick Check:

   Braces required for loop body [OK]

Hint: Always use braces {} for loop body [OK]

Common Mistakes:

• Omitting braces for single statement
• Misreading error as variable issue
• Confusing println with Println

5. Given this Go code, what will be the output?

sum := 0
for i := 1; i <= 5; i++ {
    if i%2 == 0 {
        continue
    }
    if sum > 5 {
        break
    }
    sum += i
}
fmt.Println(sum)

hard

A. 6

B. 9

C. 10

D. 5

Solution

1. Step 1: Trace loop with continue and break

   Loop i=1 to 5, skip even i (2,4). Add odd i to sum until sum > 5, then break.

2. Step 2: Calculate sum step-by-step

   i=1 (odd): sum=0+1=1
   i=2 (even): continue, skip
   i=3 (odd): sum=1+3=4
   i=4 (even): continue, skip
   i=5 (odd): sum=4+5=9 but before adding, sum=4 which is not >5, so add 5 sum=9. Now sum >5, break after this iteration.

3. Step 3: Check when break occurs

   Break happens after sum=9, but condition checks sum >5 before adding i=5, so sum was 4 before adding 5. Actually, break triggers only if sum >5 before adding i.

4. Step 4: Correct calculation

   At i=5, sum=4 (not >5), so add 5 sum=9. Next iteration would be i=6 (loop ends). So break never triggers because sum >5 check is before adding i.

5. Final Answer:

   9 -> Option B

6. Quick Check:

   Sum after adding odd numbers until break = 9 [OK]

Hint: Check continue and break order carefully [OK]

Common Mistakes:

• Adding after break condition incorrectly
• Ignoring continue skipping even numbers
• Misunderstanding break timing