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## C Program to Build a Simple Calculator Using Switch Case In this tutorial, you will learn how to create a simple arithmetic calculator in C using the `switch...case` statement. This program takes an operator (`+`, `-`, `*`, `/`) and two operands from the user, performs the corresponding mathematical operation, and displays the result. --- ### Introduction to the `switch...case` Statement The `switch` statement in C is a multi-way branch statement. It provides an elegant way to dispatch execution to different parts of code based on the value of an expression. Using `switch...case` is highly efficient and readable when you need to compare a single variable (like our operator character) against multiple constant values, making it the perfect choice for building a command-based utility like a calculator. --- ### C Source Code Below is the complete, ready-to-run C program. The program uses `double` data types to support both integer and floating-point calculations. ```c #include int main() { char operator; double firstNumber, secondNumber; // Step 1: Ask the user to input the desired operator printf("Enter an operator (+, -, *, /): "); scanf("%c", &operator); // Step 2: Ask the user to input two operands printf("Enter two numbers: "); scanf("%lf %lf", &firstNumber, &secondNumber); // Step 3: Perform the calculation based on the operator switch(operator) { case '+': printf("%.1lf + %.1lf = %.1lf\n", firstNumber, secondNumber, firstNumber + secondNumber); break; case '-': printf("%.1lf - %.1lf = %.1lf\n", firstNumber, secondNumber, firstNumber - secondNumber); break; case '*': printf("%.1lf * %.1lf = %.1lf\n", firstNumber, secondNumber, firstNumber * secondNumber); break; case '/': // Check for division by zero if (secondNumber != 0.0) { printf("%.1lf / %.1lf = %.1lf\n", firstNumber, secondNumber, firstNumber / secondNumber); } else { printf("Error! Division by zero is not allowed.\n"); } break; // If the operator does not match any case constant (+, -, *, /) default: printf("Error! The operator is not correct.\n"); } return 0; } ``` --- ### How the Code Works 1. **Variable Declaration**: * `char operator;` stores the arithmetic operator entered by the user. * `double firstNumber, secondNumber;` store the two numbers for the calculation. We use `double` to handle decimal values with high precision. 2. **User Input**: * `scanf("%c", &operator);` reads the character input. * `scanf("%lf %lf", &firstNumber, &secondNumber);` reads two floating-point numbers. 3. **The Switch Evaluation**: * The program evaluates the value of the `operator` variable. * It matches the character with the corresponding `case` label (`'+'`, `'-'`, `'*'`, `'/'`). * The `break` statement at the end of each case prevents "fall-through" execution into the next case. 4. **Default Case**: * If the user enters an operator other than the four specified, the `default` block executes, printing an error message. --- ### Example Output #### Example 1: Multiplication ```text Enter an operator (+, -, *, /): * Enter two numbers: 4 5 4.0 * 5.0 = 20.0 ``` #### Example 2: Division ```text Enter an operator (+, -, *, /): / Enter two numbers: 15.5 2 15.5 / 2.0 = 7.8 ``` #### Example 3: Invalid Operator ```text Enter an operator (+, -, *, /): % Enter two numbers: 4 5 Error! The operator is not correct. ``` --- ### Key Considerations & Best Practices * **Format Specifiers**: We use `%lf` in `scanf` to read a `double` value, and `%.1lf` in `printf` to display the double value rounded to one decimal place. * **Division by Zero**: In mathematics, dividing a number by zero is undefined. In production-grade code, always include a conditional check (`if (secondNumber != 0.0)`) inside the division case to prevent runtime errors or crashes. * **Buffer Issues with `scanf`**: If you expand this program to run in a loop, be aware that `scanf("%c", &operator)` might read leftover newline characters (`\n`) from the input buffer. Adding a leading space in the format string like `scanf(" %c", &operator)` can help bypass whitespace issues.