For loop basics in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic structure of a for loop in Go?

A for loop in Go has three parts separated by semicolons: initialization, condition, and post statement. It looks like:

for i := 0; i < 5; i++ {
    // code to repeat
}

beginner

How do you write an infinite loop using for in Go?

You write a for loop without any condition or statements:

for {
    // code runs forever
}

beginner

Can a for loop in Go be used like a while loop?

Yes! If you only provide a condition without initialization and post statements, it works like a while loop:

for i < 10 {
    // code
}

beginner

What happens if the condition in a for loop is false at the start?

The loop body does not run at all. The program skips the loop and continues after it.

beginner

How do you stop a for loop early in Go?

Use the break statement inside the loop to exit it immediately.

Which part of the for loop runs first in Go?

A Post statement

B Condition check

C Loop body

D Initialization

The initialization runs first, then the condition is checked before running the loop body.

What does this loop do?

for i := 0; i < 3; i++ { fmt.Println(i) }

A Prints 0, 1, 2

B Prints 1, 2, 3

C Prints 0, 1, 2, 3

D Prints nothing

The loop starts at 0 and runs while i is less than 3, printing 0, 1, and 2.

How do you write a loop that runs forever in Go?

A for i := 0; i < 10; i++ {}

B for {}

C while true {}

D loop forever {}

In Go, a bare `for` loop (`for {}`) runs forever.

What keyword stops a for loop immediately?

A break

B exit

C stop

D continue

break exits the loop immediately. continue skips to the next iteration.

Which of these is a valid for loop condition in Go?

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

B for (i = 0; i &lt; 5; i++) {}

C for i := 0; i &lt; 5; i++ {}

D for i < 5; i++ {}

Go uses := for initialization and semicolons to separate parts. Parentheses are not used.

Explain how a for loop works in Go and write a simple example that prints numbers 1 to 5.

Think about how you start, check, and update the loop variable.

Describe how to create an infinite loop in Go and how to stop it safely.

Remember the simplest for loop form and how to exit loops.

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