C Program To Make A Simple Calculator Using If Else

This article will guide you through creating a simple calculator program in C using if-else statements. You will learn how to accept user input for numbers and an arithmetic operator, then perform the calculation and display the result.

Problem Statement

Developing a basic calculator is a fundamental exercise in programming that helps solidify understanding of input/output operations, conditional logic, and arithmetic operations. The challenge is to correctly process two numbers and a chosen operation (addition, subtraction, multiplication, or division) to produce the accurate result.

Example

Here is what the calculator program's output will look like when run:

Enter an operator (+, -, *, /): +
Enter two operands: 10
5
Result: 10.0 + 5.0 = 15.0

Background & Knowledge Prerequisites

To follow this article effectively, a basic understanding of the following C programming concepts is beneficial:

• Variables: Declaring and using variables of different data types (e.g., double for numbers, char for the operator).
• Input/Output: Using scanf() to read user input and printf() to display output.
• Arithmetic Operators: Familiarity with +, -, *, /.
• Conditional Statements: Understanding the if-else if-else structure for decision-making.

No special libraries or complex setups are required beyond a standard C compiler (like GCC).

Use Cases or Case Studies

A simple calculator program, while basic, forms the foundation for many computational tasks:

• Educational Tool: It's an excellent project for beginners to grasp core programming logic.
• Quick Calculations: For everyday arithmetic in command-line environments.
• Embedded Systems: Basic arithmetic functions are often integrated into microcontrollers for simple data processing.
• Part of Larger Applications: Calculator logic can be a component within more complex applications, such as financial tools or engineering simulations.

Solution Approaches

This section details how to implement a simple calculator using the if-else if-else structure.

Simple Calculator using if-else

This approach involves reading the operator and two numbers from the user, then using a series of if-else if-else statements to check the operator and perform the corresponding arithmetic operation.

Code Example

// Simple Calculator
#include <stdio.h>

int main() {
    char operator_char;
    double num1, num2, result;

    // Step 1: Prompt user for the operator
    printf("Enter an operator (+, -, *, /): ");
    scanf(" %c", &operator_char); // Note the space before %c to consume newline

    // Step 2: Prompt user for two operands
    printf("Enter two operands: ");
    scanf("%lf %lf", &num1, &num2);

    // Step 3: Use if-else if-else to perform calculation based on operator
    if (operator_char == '+') {
        result = num1 + num2;
        printf("Result: %.1lf %c %.1lf = %.1lf\\n", num1, operator_char, num2, result);
    } else if (operator_char == '-') {
        result = num1 - num2;
        printf("Result: %.1lf %c %.1lf = %.1lf\\n", num1, operator_char, num2, result);
    } else if (operator_char == '*') {
        result = num1 * num2;
        printf("Result: %.1lf %c %.1lf = %.1lf\\n", num1, operator_char, num2, result);
    } else if (operator_char == '/') {
        // Handle division by zero
        if (num2 != 0) {
            result = num1 / num2;
            printf("Result: %.1lf %c %.1lf = %.1lf\\n", num1, operator_char, num2, result);
        } else {
            printf("Error! Division by zero is not allowed.\\n");
        }
    } else {
        printf("Error! Invalid operator entered.\\n");
    }

    return 0;
}

Run

Sample Output

Enter an operator (+, -, *, /): *
Enter two operands: 12.5
2
Result: 12.5 * 2.0 = 25.0

Enter an operator (+, -, *, /): /
Enter two operands: 10
0
Error! Division by zero is not allowed.

Stepwise Explanation

1. Declare Variables:

• char operator_char;: Stores the arithmetic operator entered by the user.
• double num1, num2, result;: Store the two floating-point numbers (operands) and the calculated result. double is used to handle decimal values.

1. Get Operator Input:

• printf("Enter an operator (+, -, *, /): ");: Prompts the user to enter an operator.
• scanf(" %c", &operator_char);: Reads the character entered by the user. The space before %c is crucial; it tells scanf to consume any whitespace characters (like the newline character left in the buffer from a previous input) before reading the actual character.

1. Get Operand Input:

• printf("Enter two operands: ");: Prompts the user for the numbers.
• scanf("%lf %lf", &num1, &num2);: Reads two double values from the user and stores them in num1 and num2.

1. Perform Calculation with if-else if-else:

• The program enters a series of if-else if-else statements.
• Each if or else if condition checks if operator_char matches a specific operator (+, -, *, /).
• If a match is found, the corresponding arithmetic operation is performed, and the result is calculated.
• For division (/), an additional if (num2 != 0) check is included to prevent "division by zero" errors, which would crash the program. If num2 is zero, an error message is printed.
• The final else block catches any invalid operator input, informing the user.
• printf("Result: %.1lf %c %.1lf = %.1lf\n", num1, operator_char, num2, result);: This line displays the input numbers, the operator, and the calculated result, formatted to one decimal place (.1lf).

1. Return 0: Indicates successful program execution.

Conclusion

Building a simple calculator using if-else statements is an effective way to learn conditional logic and basic input/output in C programming. This approach clearly demonstrates how to handle different user choices and provides a robust structure to prevent common errors like division by zero, all within a straightforward and understandable code block.

Summary

• A basic C calculator uses scanf() for input and printf() for output.
• The if-else if-else structure is key for selecting the correct arithmetic operation based on the user's operator choice.
• Error handling for division by zero (num2 != 0) is essential for program stability.
• Using double for numbers allows for decimal calculations.
• The %c format specifier in scanf (with a leading space) helps consume leftover newline characters from previous inputs, ensuring correct character input.