Increment and decrement in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of increment in a loop

What is the output of this Go program?

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

Go

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

A 3

B 0

C 1

D Syntax error

💡 Hint

Think about how many times the loop runs and how x changes each time.

The loop runs 3 times, and each time x is increased by 1 using x++. So final x is 3.

❓ Predict Output

intermediate

Decrement operator effect

What will this Go program print?

package main
import "fmt"
func main() {
  y := 5
  y--
  fmt.Println(y)
}

Go

package main
import "fmt"
func main() {
  y := 5
  y--
  fmt.Println(y)
}

A 5

B 6

C 4

D Compilation error

💡 Hint

Decrement means subtracting one from the variable.

y starts at 5, then y-- subtracts 1, so y becomes 4.

❓ Predict Output

advanced

Increment in expression

What is the output of this Go code?

package main
import "fmt"
func main() {
  a := 1
  b := a++
  fmt.Println(a, b)
}

Go

package main
import "fmt"
func main() {
  a := 1
  b := a++
  fmt.Println(a, b)
}

A Compilation error

B 1 1

C 2 1

D 1 2

💡 Hint

Go does not support post-increment as an expression.

In Go, the increment operator ++ is a statement, not an expression. So 'b := a++' causes a compilation error.

❓ Predict Output

advanced

Decrement in a for loop

What does this Go program print?

package main
import "fmt"
func main() {
  count := 3
  for count > 0 {
    fmt.Print(count, " ")
    count--
  }
}

Go

package main
import "fmt"
func main() {
  count := 3
  for count > 0 {
    fmt.Print(count, " ")
    count--
  }
}

A Compilation error

B 3 2 1

C 3 3 3

D 1 2 3

💡 Hint

The loop runs while count is greater than zero and decreases count each time.

The loop prints count starting at 3, then 2, then 1, then stops when count is 0.

🧠 Conceptual

expert

Why Go disallows increment in expressions

Why does Go language not allow using increment (++) or decrement (--) operators inside expressions like 'b := a++'?

A Because Go does not support increment or decrement operators at all.

B Because Go requires ++ and -- to be used only with pointers.

C Because Go only allows ++ and -- inside function definitions, not in main.

D Because ++ and -- are statements, not expressions, to avoid confusion and side effects in expressions.

💡 Hint

Think about how Go treats ++ and -- differently from some other languages.

Go treats ++ and -- as statements to keep code clear and avoid subtle bugs from side effects in expressions.

Practice

1. What does the expression i++ do in Go?

easy

A. Decreases the value of i by 1

B. Increases the value of i by 1

C. Multiplies the value of i by 2

D. Divides the value of i by 2

Solution

1. Step 1: Understand the operator meaning

   The ++ operator in Go adds 1 to the variable it is used on.

2. Step 2: Apply to variable i

   Using i++ increases the value of i by exactly 1.

3. Final Answer:

   Increases the value of i by 1 -> Option B

4. Quick Check:

   i++ means add 1 [OK]

Hint: Remember ++ means add one, -- means subtract one [OK]

Common Mistakes:

• Confusing ++ with --
• Thinking ++ multiplies or divides
• Using ++ as a function

2. Which of the following is the correct syntax to decrease a variable count by 1 in Go?

easy

A. count--

B. --count

C. count++

D. count =- 1

Solution

1. Step 1: Identify decrement syntax in Go

   In Go, variable-- is the correct way to subtract 1 from a variable.

2. Step 2: Check each option

   count-- uses count--, which is correct. --count is invalid prefix decrement in Go. count++ increases count. count =- 1 is invalid syntax.

3. Final Answer:

   count-- -> Option A

4. Quick Check:

   Use -- to subtract one [OK]

Hint: Use -- to subtract one, not =- [OK]

Common Mistakes:

• Using --count instead of count--
• Confusing ++ and --
• Using count += 1 to decrement

3. What is the output of this Go code?

package main
import "fmt"
func main() {
  x := 5
  x++
  x--
  x++
  fmt.Println(x)
}

medium

A. Syntax error

B. 5

C. 7

D. 6

Solution

1. Step 1: Trace the increments and decrements

   Start with x = 5. Then x++ makes x = 6. Then x-- makes x = 5 again. Then x++ makes x = 6.

2. Step 2: Print the final value

   The final value of x is 6, so fmt.Println(x) prints 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   5 +1 -1 +1 = 6 [OK]

Hint: Add and subtract step by step to find final value [OK]

Common Mistakes:

• Ignoring one increment or decrement
• Thinking increments happen before assignment
• Confusing output with syntax error

4. Find the error in this Go code snippet:

package main
func main() {
  var n int = 10
  n++
  n--
  n = n++
}

medium

A. Assigning n = n++ causes a compile error

B. n-- cannot be used on integers

C. Using n++ as a statement is invalid

D. Variable n must be declared without type

Solution

1. Step 1: Understand usage of n++ in Go

   In Go, n++ and n-- are statements that increment or decrement n by 1. They cannot be used as expressions.

2. Step 2: Analyze the assignment n = n++

   Assigning n = n++ tries to use n++ as a value, which is invalid in Go and causes a compile error.

3. Final Answer:

   Assigning n = n++ causes a compile error -> Option A

4. Quick Check:

   n++ is a statement, not an expression [OK]

Hint: Remember n++ can't be assigned; it's a statement only [OK]

Common Mistakes:

• Trying to assign n = n++
• Thinking n-- is invalid on int
• Ignoring Go's statement-only rule for ++/--

5. You want to count down from 3 to 1 using a for loop in Go. Which code correctly uses decrement to do this?

for i := 3; i > 0; ??? {
  fmt.Println(i)
}

hard

A. i += 1

B. i++

C. i--

D. --i

Solution

1. Step 1: Understand the loop goal

   The loop should count down from 3 to 1, so i must decrease each time.

2. Step 2: Choose the correct decrement expression

   Using i-- decreases i by 1 each loop, matching the goal. Options A, B, and C are wrong: A and B increase i, C is invalid prefix --i in Go.

3. Final Answer:

   i-- -> Option C

4. Quick Check:

   Use i-- to count down in loops [OK]

Hint: Use i-- to count down, i++ to count up [OK]

Common Mistakes:

• Using i++ when counting down
• Using i += 1 instead of i--
• Confusing decrement syntax in for loops