Assignment operators in C++

Introduction

Assignment operators help you store values in variables easily. They let you update or change values step by step.

When you want to save a number or text into a variable.

When you want to add or subtract a value from a variable quickly.

When you want to multiply or divide a variable by a number and save the result.

When you want to update a variable based on its current value.

Syntax

C++

variable = value;
variable += value;
variable -= value;
variable *= value;
variable /= value;
variable %= value;

The = operator sets the variable to a new value.

The other operators like += add and assign in one step.

Examples

Assign 5 to variable x.

C++

int x = 5;

Add 3 to x and save the result back to x.

C++

x += 3;  // same as x = x + 3;

Multiply x by 2 and save the result back to x.

C++

x *= 2;  // same as x = x * 2;

Set x to the remainder when x is divided by 4.

C++

x %= 4;  // same as x = x % 4;

Sample Program

This program shows how assignment operators change the value of x step by step.

C++

#include <iostream>

int main() {
    int x = 10;
    std::cout << "Initial x: " << x << "\n";

    x += 5;
    std::cout << "After x += 5: " << x << "\n";

    x -= 3;
    std::cout << "After x -= 3: " << x << "\n";

    x *= 2;
    std::cout << "After x *= 2: " << x << "\n";

    x /= 4;
    std::cout << "After x /= 4: " << x << "\n";

    x %= 3;
    std::cout << "After x %= 3: " << x << "\n";

    return 0;
}

Important Notes

Assignment operators combine math and assignment in one step to save time.

Be careful with division and modulus to avoid dividing by zero.

Summary

Assignment operators store or update values in variables.

They make code shorter and easier to read.

Common ones include =, +=, -=, *=, /=, and %=.

Practice

1. Which of the following assignment operators adds the right value to the left variable and stores the result back in the left variable?

easy

A. +=

B. =

C. -=

D. *=

Solution

1. Step 1: Understand the meaning of +=

   The operator += adds the right side value to the left side variable and updates the variable with the new value.

2. Step 2: Compare with other operators

   = assigns a value, -= subtracts, and *= multiplies. Only += adds and assigns.

3. Final Answer:

   += -> Option A

4. Quick Check:

   Add and assign = += [OK]

Hint: Remember: += means add then assign [OK]

Common Mistakes:

• Confusing = with +=
• Thinking -= adds values
• Mixing *= with addition

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 *= 5;

C. x = 5*;

D. x = 5 *;

Solution

1. Step 1: Identify the correct assignment operator syntax

   The operator to multiply and assign is *=, so x *= 5; is correct.

2. Step 2: Check other options for syntax errors

   x =* 5; and x = 5*; are invalid syntax. x = 5 *; is incomplete.

3. Final Answer:

   x *= 5; -> Option B

4. Quick Check:

   Multiply and assign = *= [OK]

Hint: Use operator before = for combined assignment [OK]

Common Mistakes:

• Placing * after = instead of before
• Leaving incomplete expressions
• Confusing with simple assignment =

3. What is the output of the following code?

int a = 10;
a += 5;
a -= 3;
std::cout << a;

medium

A. 12

B. 15

C. 8

D. 10

Solution

1. Step 1: Calculate a += 5;

   Starting with a = 10, adding 5 gives a = 15.

2. Step 2: Calculate a -= 3;

   Subtracting 3 from 15 gives a = 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   10 + 5 - 3 = 12 [OK]

Hint: Apply each assignment step by step [OK]

Common Mistakes:

• Adding and subtracting in wrong order
• Confusing += and -= effects
• Ignoring the updated value after first operation

4. Identify the error in the following code snippet:

int x = 7;
x =+ 3;
std::cout << x;

medium

A. Syntax error due to incorrect operator

B. x will be 10

C. x will be 3

D. No error, output is 10

Solution

1. Step 1: Analyze x =+ 3;

   This is not the addition assignment +=. Instead, =+ means assign positive 3 to x.

2. Step 2: Determine the value of x after assignment

   x becomes 3, not 10, because =+ is just assignment with unary plus.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   =+ is assignment, not addition [OK]

Hint: Watch for =+ vs += difference [OK]

Common Mistakes:

• Confusing =+ with += operator
• Expecting addition instead of assignment
• Assuming output is sum without checking syntax

5. Given int n = 20;, which code snippet correctly divides n by 4 and then subtracts 2 from the result, updating n accordingly?

hard

A. n = n - 2 / 4;

B. n -= 2; n /= 4;

C. n = (n - 2) / 4;

D. n /= 4; n -= 2;

Solution

1. Step 1: Understand the required operations order

   First divide n by 4, then subtract 2 from the result, updating n each time.

2. Step 2: Check each option

   n /= 4; n -= 2; does n /= 4; then n -= 2;, matching the requirement. n -= 2; n /= 4; reverses order. n = (n - 2) / 4; subtracts first due to parentheses (18 / 4 = 4). n = n - 2 / 4; subtracts incorrectly.

3. Step 3: Confirm correct update

   n /= 4; n -= 2; updates n stepwise as requested.

4. Final Answer:

   n /= 4; n -= 2; -> Option D

5. Quick Check:

   Divide then subtract = n /= 4; n -= 2; [OK]

Hint: Follow operation order exactly [OK]

Common Mistakes:

• Reversing operation order
• Misunderstanding combined expressions
• Incorrect operator precedence assumptions