Assignment operators in Go - Step-by-Step Execution

Concept Flow - Assignment operators

Start

↓

Declare variable

↓

Assign value with =

↓

Use compound assignment (+=, -=, etc.)?

No→End

Yes↓

Update variable value

↓

Continue or End

This flow shows how variables are declared and assigned values, then optionally updated using compound assignment operators.

Execution Sample

Go

package main
import "fmt"
func main() {
  x := 5
  x += 3
  fmt.Println(x)
}

This Go code declares a variable x, adds 3 to it using the += operator, and prints the result.

Execution Table

Step	Code Line	Variable	Operation	Value After Operation	Output
1	x := 5	x	Declare and assign	5
2	x += 3	x	Add 3 to x	8
3	fmt.Println(x)	x	Print value	8	8

💡 Program ends after printing the updated value of x.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	undefined	5	8	8

Key Moments - 2 Insights

Why does x change from 5 to 8 after the += operation?

Because the += operator adds the right side value (3) to the current value of x (5), updating x to 8 as shown in execution_table step 2.

What would happen if we used = instead of += in step 2?

Using = would assign the right side value directly to x, so if it was x = 3, x would become 3 instead of adding to 5. The execution_table would show x changing to 3 at step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of x after step 1?

A 5

B 8

C 0

D undefined

💡 Hint

Check the 'Value After Operation' column for step 1 in the execution_table.

At which step does x get updated by adding 3?

A Step 1

B Step 2

C Step 3

D Never

💡 Hint

Look at the 'Operation' column in execution_table to find when += is applied.

If we replaced 'x += 3' with 'x = 10', what would be the final value of x?

A 5

B 8

C 10

D 3

💡 Hint

Assignment with = sets the variable directly, so x would be 10 after that line.

Concept Snapshot

Assignment operators in Go:
- Use = to assign values.
- Use +=, -=, *=, /=, %= to update variables by applying an operation.
- Example: x += 3 adds 3 to x.
- They simplify code by combining operation and assignment.
- Variables must be declared before assignment.

Full Transcript

This example shows how assignment operators work in Go. First, a variable x is declared and assigned the value 5. Then, using the += operator, 3 is added to x, updating its value to 8. Finally, the program prints the value of x, which is 8. The execution table traces each step, showing how x changes. Key points include understanding that += adds to the current value, and that using = assigns a new value directly. The visual quiz tests understanding of these steps and outcomes.

Practice

1. What does the += operator do in Go?

easy

A. Subtracts the right value from the left variable and stores the result

B. Assigns the right value to the left variable without any operation

C. Adds the right value to the left variable and stores the result in the left variable

D. Multiplies the left variable by the right value and stores the result

Solution

1. Step 1: Understand the operator meaning

   The += operator adds the right-hand side value to the left-hand side variable.

2. Step 2: Understand the assignment effect

   It then stores the sum back into the left-hand side variable, updating its value.

3. Final Answer:

   Adds and assigns the sum to the left variable -> Option C

4. Quick Check:

   += means add and assign [OK]

Hint: Think: add right value to left and save [OK]

Common Mistakes:

• Confusing += with simple assignment =
• Thinking it subtracts instead of adds
• Mixing it with multiplication or division

2. Which of the following is the correct syntax to multiply variable x by 5 and store the result back in x?

easy

A. x =* 5

B. x = x *=

C. x = *5

D. x *= 5

Solution

1. Step 1: Identify correct compound assignment syntax

   In Go, the multiplication assignment operator is *=, used as x *= 5.

2. Step 2: Check each option for syntax correctness

   x *= 5 matches the correct syntax; others are invalid or cause errors.

3. Final Answer:

   x *= 5 -> Option D

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Remember operator before = for compound assignment [OK]

Common Mistakes:

• Placing = before * (like =*)
• Missing space causing syntax errors
• Using incomplete expressions like x = *5

3. What is the output of the following Go code?

package main
import "fmt"
func main() {
  a := 10
  a += 5
  a -= 3
  fmt.Println(a)
}

medium

A. 12

B. 15

C. 8

D. 10

Solution

1. Step 1: Calculate after addition

   Starting with a = 10, after a += 5, a becomes 15.

2. Step 2: Calculate after subtraction

   Then a -= 3 subtracts 3, so a becomes 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   10 + 5 - 3 = 12 [OK]

Hint: Apply operations step-by-step to variable [OK]

Common Mistakes:

• Adding and subtracting in wrong order
• Confusing += and -= effects
• Ignoring initial value of variable

4. Identify the error in this Go code snippet:

package main
import "fmt"
func main() {
  var x int = 10
  x + = 5
  fmt.Println(x)
}

medium

A. The operator + = has a space and is invalid

B. Variable x is not declared

C. Missing semicolon after var declaration

D. fmt package is not imported

Solution

1. Step 1: Check operator syntax

   The operator += must not have spaces; + = is invalid syntax.

2. Step 2: Verify other code parts

   Variable x is declared correctly, semicolons are optional in Go, and the fmt package is imported.

3. Final Answer:

   Operator + = has a space and is invalid -> Option A

4. Quick Check:

   No spaces in compound operators [OK]

Hint: Compound operators have no spaces (e.g., +=) [OK]

Common Mistakes:

• Adding spaces inside operators
• Assuming semicolons are always required
• Confusing the compound operator with separate + and = operations

5. Given the code below, what will be the final value of total?

package main
import "fmt"
func main() {
  total := 20
  total /= 4
  total *= 3
  total %= 5
  fmt.Println(total)
}

hard

A. 3

B. 0

C. 4

D. 5

Solution

1. Step 1: Perform division assignment

   total = 20, after total /= 4, total becomes 5 (integer division).

2. Step 2: Perform multiplication assignment

   Then total *= 3 makes total 15.

3. Step 3: Perform modulus assignment

   total %= 5 calculates remainder of 15 divided by 5, which is 0.

4. Step 4: Re-check calculations

   Integer division 20/4 = 5, 5*3=15, 15%5=0.

5. Final Answer:

   0 -> Option B

6. Quick Check:

   20/4=5, 5*3=15, 15%5=0 [OK]

Hint: Apply each operator stepwise, watch integer division [OK]

Common Mistakes:

• Forgetting integer division truncates decimals
• Mixing up modulus with division
• Calculating modulus before multiplication