For loop basics in Go - Step-by-Step Execution

Concept Flow - For loop basics

Initialize i=0

↓

Check: i < 5?

No→EXIT

Yes↓

Execute body

↓

Update: i = i+1

↩Back to Check

The loop starts by setting i to 0, then checks if i is less than 5. If yes, it runs the loop body, then increases i by 1 and repeats. If no, it stops.

Execution Sample

Go

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

This code prints numbers from 0 to 4 using a for loop.

Execution Table

Iteration	i	Condition i<5	Action	Output
1	0	true	Print i=0, i++	0
2	1	true	Print i=1, i++	1
3	2	true	Print i=2, i++	2
4	3	true	Print i=3, i++	3
5	4	true	Print i=4, i++	4
6	5	false	Exit loop

💡 i reaches 5, condition 5 < 5 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
i	0	1	2	3	4	5	5

Key Moments - 3 Insights

Why does the loop stop when i equals 5?

Because the condition i < 5 becomes false at iteration 6, as shown in the execution_table row 6.

Does the loop print the number 5?

No, the loop stops before printing 5 because the condition i < 5 is false when i is 5, as seen in execution_table row 6.

When is the variable i increased?

i is increased after printing in each iteration, before the next condition check, as shown in the Action column of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i during iteration 3?

A 2

B 3

C 1

D 0

💡 Hint

Check the 'i' column in execution_table row 3.

At which iteration does the condition i < 5 become false?

A 5

B 6

C 4

D 1

💡 Hint

Look at the 'Condition i<5' column in execution_table row 6.

If we change the loop to i < 3, how many times will the loop run?

A 2 times

B 5 times

C 3 times

D 4 times

💡 Hint

Compare the condition i < 5 with i < 3 and count iterations accordingly.

Concept Snapshot

Go for loop syntax:
for initialization; condition; post {
    // code
}
Loop runs while condition is true.
Variable updates after each iteration.
Stops when condition is false.

Full Transcript

This visual trace shows a Go for loop starting with i=0. Each step checks if i is less than 5. If true, it prints i and then increases i by 1. This repeats until i reaches 5, when the condition fails and the loop stops. The variable tracker shows i's value changing from 0 up to 5. Key moments clarify why the loop stops before printing 5 and when i increments. The quiz tests understanding of variable values and loop stopping conditions.

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