Loop execution flow in Go - Step-by-Step Execution

Concept Flow - Loop execution flow

Initialize loop variable i=0

↓

Check condition i < 3?

No→Exit loop

Yes↓

Execute loop body

↓

Update loop variable i = i + 1

↩Back to condition check

The loop starts by setting a variable, checks if it meets the condition, runs the loop body if yes, then updates the variable and repeats until the condition is false.

Execution Sample

Go

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

This Go program prints numbers 0, 1, and 2 using a for loop.

Execution Table

Step	i value	Condition (i < 3)	Action	Output
1	0	true	Print i=0	0
2	1	true	Print i=1	1
3	2	true	Print i=2	2
4	3	false	Exit loop

💡 Loop stops because i=3 is not less than 3 (condition false)

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	0	1	2	3	3

Key Moments - 2 Insights

Why does the loop stop when i equals 3?

Because the condition i < 3 becomes false at step 4 in the execution_table, so the loop exits.

When is the value of i updated in the loop?

After each loop body execution, i is increased by 1 as shown between steps in the variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i when the loop condition becomes false?

A 3

B 2

C 0

D 1

💡 Hint

Check the last row of the execution_table where condition is false.

At which step does the loop print the number 1?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the Output column in execution_table for the printed values.

If the loop condition changed to i < 2, how many times would the loop run?

A 1 time

B 2 times

C 3 times

D 0 times

💡 Hint

Refer to variable_tracker and consider when the condition becomes false.

Concept Snapshot

Go for loop syntax:
for initialization; condition; post {
  // loop body
}

Loop runs while condition is true.
Variable updates happen after each iteration.
Loop stops when condition is false.

Full Transcript

This visual execution shows a Go for loop starting with i=0. Each step checks if i is less than 3. If yes, it prints i and then increases i by 1. This repeats until i reaches 3, when the condition fails and the loop stops. The variable tracker shows i changing from 0 to 3. Key moments clarify why the loop stops at 3 and when i updates. The quiz tests understanding of loop steps and condition changes.

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