Understanding the *= (Multiplication Assignment) Operator in C: A Beginner’s Guide

In C programming, the *= operator is a shorthand for multiplying a variable by a value and then storing the result back into that variable. This operator is part of the compound assignment operators, which provide a more concise and readable way to update the value of a variable based on an arithmetic operation. The *= operator is commonly used in loops, calculations, and situations where a variable needs to be multiplied by a constant or another variable.

In this blog, we will break down the *= operator, explore its syntax, behavior, and practical examples, and discuss how it can be effectively used to simplify your C code.

1. What is the *= Operator?

The *= (multiplication assignment) operator performs two actions:

1. Multiplies the left-hand operand by the right-hand operand.
2. Assigns the result of the multiplication back to the left-hand operand.

Syntax

variable *= value;

• variable: The variable to which the result of the multiplication will be assigned.
• value: The value that will be multiplied by the variable.

This is equivalent to the longer form:

variable = variable * value;

However, the *= operator provides a more concise and cleaner way to express the same operation.

2. Basic Usage

The *= operator is most commonly used in situations where you need to scale or increase the value of a variable based on multiplication.

Example 1: Simple Multiplication

#include <stdio.h>
 
int main() {
    int total = 5;
    total *= 3;  // Multiplies total by 3, so total becomes 15
    printf("The total is: %d\n", total);
    return 0;
}

Output:
The total is: 15

Explanation:
The *= operator multiplies total (which is initially 5) by 3, resulting in 15.

Example 2: Using *= in a Loop

#include <stdio.h>
 
int main() {
    int product = 1;
    for (int i = 1; i <= 5; i++) {
        product *= i;  // Multiplies product by i on each iteration
    }
    printf("The product is: %d\n", product);
    return 0;
}

Output:
The product is: 120

Explanation:
The product is multiplied by each number in the loop (from 1 to 5). At the end of the loop, product holds the result of 1 * 2 * 3 * 4 * 5, which equals 120.

3. Combining *= with Other Operators

The *= operator can also be used in combination with other arithmetic operators to perform more complex expressions.

Example: Using *= with Addition

#include <stdio.h>
 
int main() {
    int value = 10;
    value *= 2 + 3;  // Multiplies value by (2 + 3), so value becomes 50
    printf("The updated value is: %d\n", value);
    return 0;
}

Output:
The updated value is: 50

Explanation:
The expression 2 + 3 is evaluated first (due to operator precedence), resulting in 5. Then, value (which was 10) is multiplied by 5, giving the result 50.

4. Operator Precedence and Associativity

The *= operator follows the same precedence as the multiplication operator (*). It is evaluated after addition and subtraction but before assignment operators.

Precedence Order (High to Low):

1. Arithmetic operators (*, /, +, -)
2. Assignment operators (*=, /=, +=, etc.)

Example: Precedence Demonstration

#include <stdio.h>
 
int main() {
    int result = 3 + 2 * 5;  // Multiplication happens first, then addition
    printf("Result: %d\n", result);
    return 0;
}

Output:
Result: 13

Explanation:
In the expression 3 + 2 * 5, multiplication (2 * 5) is performed first because of operator precedence. After that, 3 is added to the result of the multiplication, giving 13.

5. Shortened Syntax and Readability

Using the *= operator allows you to make your code more concise, particularly in loops or calculations that involve repeated multiplication. It eliminates the need to repeat the variable on both sides of the assignment, making the code easier to read and maintain.

Example: Without *= Operator

#include <stdio.h>
 
int main() {
    int total = 1;
    for (int i = 1; i <= 5; i++) {
        total = total * i;  // Without using *=
    }
    printf("The product is: %d\n", total);
    return 0;
}

Output:
The product is: 120

Explanation:
This code achieves the same result as the previous loop example, but it is more verbose and harder to read.

Example: With *= Operator

#include <stdio.h>
 
int main() {
    int total = 1;
    for (int i = 1; i <= 5; i++) {
        total *= i;  // Using *= for conciseness
    }
    printf("The product is: %d\n", total);
    return 0;
}

Output:
The product is: 120

Explanation:
By using the *= operator, the code is cleaner, more concise, and easier to read.

6. Edge Cases and Special Scenarios

Edge Case 1: Multiplying by Zero

#include <stdio.h>
 
int main() {
    int number = 10;
    number *= 0;  // Multiplies number by 0, so number becomes 0
    printf("The number is: %d\n", number);
    return 0;
}

Output:
The number is: 0

Explanation:
Multiplying any number by zero results in 0, so the final value of number is 0.

Edge Case 2: Multiplying by One

#include <stdio.h>
 
int main() {
    int number = 10;
    number *= 1;  // Multiplies number by 1, so number remains 10
    printf("The number is: %d\n", number);
    return 0;
}

Output:
The number is: 10

Explanation:
Multiplying any number by 1 does not change its value, so number remains 10.

Edge Case 3: Negative Values

#include <stdio.h>
 
int main() {
    int number = -10;
    number *= 3;  // Multiplies number by 3, so number becomes -30
    printf("The number is: %d\n", number);
    return 0;
}

Output:
The number is: -30

Explanation:
Multiplying a negative number by a positive number results in a negative product.

7. Common Mistakes to Avoid

Mistake 1: Confusing *= with = (Assignment)

Remember that the *= operator is for multiplication and assignment in one step, whereas the = operator is for simple assignment. Make sure you use the correct operator for the operation you intend.

Mistake 2: Using *= with Incorrect Data Types

Ensure that you are multiplying compatible data types. For example, trying to use *= with a non-numeric type will result in a compilation error.

8. Important Points to Remember

• Shorthand for Multiplication: The *= operator is a shorthand way to multiply a variable by a value and store the result in the variable.
• Precedence: The *= operator follows the same precedence as the multiplication operator (*), meaning multiplication happens before assignment.
• Concise and Readable Code: Using *= can make your code more concise, especially in loops or cumulative multiplication operations.
• Multiplying by Zero or One: Multiplying by zero always results in zero, and multiplying by one leaves the value unchanged.

Summary

The *= operator is a powerful tool for simplifying multiplication and assignment operations in C. By understanding its behavior, precedence, and common use cases, you can write cleaner, more efficient code. Whether you’re working with loops, scaling variables, or performing repeated multiplications, the *= operator can help you reduce redundancy and improve readability in your C programs.