Respect Order of Operations in C

Introduction

In this lab, you will learn how to respect the order of operations in C programming when performing basic arithmetic operations. You will start by declaring variables and forming an expression, then explore how to use parentheses to control the evaluation order. Finally, you will print the final result to observe the impact of the order of operations. This lab covers the fundamental concepts of basic arithmetic operations in C, which are essential for building more complex programs.

Skills Graph

Declare Variables and Form an Expression

In this step, you'll learn how to declare variables and create an arithmetic expression in C that demonstrates the order of operations.

First, create a new C file in the ~/project directory:

cd ~/project
nano order_of_operations.c

Now, enter the following code:

#include <stdio.h>

int main() {
    int a = 10;
    int b = 5;
    int c = 3;

    int result = a + b * c;

    printf("Result of a + b * c: %d\n", result);

    return 0;
}

Let's break down the code:

• We declare three integer variables: a, b, and c
• We create an expression a + b * c that will demonstrate the default order of operations
• The printf statement will output the result of this calculation

Compile and run the program:

gcc order_of_operations.c -o order_of_operations
./order_of_operations

Example output:

Result of a + b * c: 25

In this example, multiplication (b * c) is performed before addition (a + ...) due to the standard order of operations in C. The calculation is equivalent to a + (b * c), which is 10 + (5 * 3) = 10 + 15 = 25.

Use Parentheses to Control Evaluation Order

In this step, you'll learn how to use parentheses to change the order of operations in C arithmetic expressions.

Open the previous file to modify the code:

cd ~/project
nano order_of_operations.c

Replace the previous code with the following:

#include <stdio.h>

int main() {
    int a = 10;
    int b = 5;
    int c = 3;

    // Using parentheses to change evaluation order
    int result_with_parentheses = a + (b * c);
    int result_without_parentheses = a + b * c;

    printf("Result with parentheses (a + (b * c)): %d\n", result_with_parentheses);
    printf("Result without parentheses (a + b * c): %d\n", result_without_parentheses);

    return 0;
}

Compile and run the program:

gcc order_of_operations.c -o order_of_operations
./order_of_operations

Example output:

Result with parentheses (a + (b * c)): 25
Result without parentheses (a + b * c): 25

In this example:

• a + (b * c) explicitly shows the multiplication happening first
• The result is the same as the previous example because the default order of operations already performs multiplication before addition
• Parentheses help make the intended order of operations clear and can change calculations in more complex expressions

Print the Final Result

In this step, you'll expand on the previous example by creating a more complex arithmetic expression and printing detailed results to demonstrate the order of operations.

Open the file to modify the code:

cd ~/project
nano order_of_operations.c

Replace the previous code with the following:

#include <stdio.h>

int main() {
    int a = 10;
    int b = 5;
    int c = 3;
    int d = 2;

    // Complex expression with multiple operations
    int result_default = a + b * c - d;
    int result_with_parentheses = a + (b * c - d);

    printf("Original Expression Breakdown:\n");
    printf("a = %d, b = %d, c = %d, d = %d\n", a, b, c, d);

    printf("\nDefault Evaluation (a + b * c - d):\n");
    printf("Step 1: b * c = %d\n", b * c);
    printf("Step 2: a + (b * c) = %d\n", a + (b * c));
    printf("Step 3: (a + b * c) - d = %d\n", result_default);

    printf("\nParentheses Evaluation (a + (b * c - d)):\n");
    printf("Step 1: b * c - d = %d\n", b * c - d);
    printf("Step 2: a + (b * c - d) = %d\n", result_with_parentheses);

    return 0;
}

Compile and run the program:

gcc order_of_operations.c -o order_of_operations
./order_of_operations

Example output:

Original Expression Breakdown:
a = 10, b = 5, c = 3, d = 2

Default Evaluation (a + b * c - d):
Step 1: b * c = 15
Step 2: a + (b * c) = 25
Step 3: (a + b * c) - d = 23

Parentheses Evaluation (a + (b * c - d)):
Step 1: b * c - d = 13
Step 2: a + (b * c - d) = 23

Key points:

• The code demonstrates how parentheses can change the order of operations
• We show step-by-step evaluation of the expressions
• Both expressions ultimately result in the same value (23)

Summary

In this lab, you learned how to respect the order of operations in C programming. First, you declared variables and formed an arithmetic expression to demonstrate the default order of operations, where multiplication is performed before addition. Then, you used parentheses to control the evaluation order and change the result of the expression. By understanding the importance of order of operations and using parentheses effectively, you can write more accurate and predictable C programs.