C Subtraction Assignment Operator

In C, the Subtraction Assignment -= operator is a shorthand operator used to subtract a value from a variable and assign the result back to that variable.

Subtraction Assignment is equivalent to writing variable = variable - value. This operator is useful for reducing code redundancy and improving readability.

Syntax of the Subtraction Assignment Operator

The syntax to use the Subtraction Assignment operator is:

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variable -= value;

Explanation:

  1. variable: The operand whose value will be updated.
  2. -=: The subtraction assignment operator.
  3. value: The value to be subtracted from variable.
  4. The operation variable -= value is equivalent to variable = variable - value.

Examples of the Subtraction Assignment Operator

1. Basic Usage of the Subtraction Assignment Operator

In this example, we will demonstrate the basic use of the -= operator by subtracting a value from an integer variable.

main.c

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#include <stdio.h>

int main() {
    int num = 20;
    num -= 5; // Equivalent to num = num - 5

    printf("Result: %d\n", num);

    return 0;
}

Explanation:

  1. We declare an integer variable num and initialize it with 20.
  2. The statement num -= 5 subtracts 5 from num and assigns the new value to num.
  3. The final value of num is 15, which is printed using printf().

Output:

Result: 15

2. Using Subtraction Assignment in a Loop

In this example, we will use the -= operator inside a loop to decrease a variable’s value repeatedly.

main.c

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#include <stdio.h>

int main() {
    int count = 10;

    while (count > 0) {
        printf("%d ", count);
        count -= 2; // Subtract 2 in each iteration
    }

    return 0;
}

Explanation:

  1. We declare an integer variable count and initialize it with 10.
  2. The while loop runs as long as count is greater than 0.
  3. Inside the loop, the value of count is printed.
  4. The count -= 2 statement reduces the value of count by 2 in each iteration.
  5. The loop terminates when count becomes 0 or negative.

Output:

10 8 6 4 2

3. Subtracting Float Values Using Subtraction Assignment

In this example, we will use the -= operator with floating-point numbers.

main.c

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#include <stdio.h>

int main() {
    float price = 50.75;
    price -= 10.25; // Subtracting 10.25 from price

    printf("Final Price: %.2f\n", price);

    return 0;
}

Explanation:

  1. We declare a floating-point variable price and initialize it with 50.75.
  2. The statement price -= 10.25 subtracts 10.25 from price and stores the result back in price.
  3. The final value of price is 40.50, which is printed using printf() with two decimal places.

Output:

Final Price: 40.50

Conclusion

In this tutorial, we covered the Subtraction Assignment -= operator in C:

  1. The -= operator subtracts a value from a variable and assigns the result back to that variable.
  2. It simplifies expressions like variable = variable - value.
  3. It can be used with different data types, such as integers and floating-point numbers.
  4. It is useful in loops and mathematical operations.