Guided: Control Structures and Functions in C

Welcome to this C++ lab where you will build a command-line calculator from scratch. You will use control structures—such as if, else, for, and while—to direct your program’s decisions and repetitions, similar to selecting operations or looping calculations in a calculator. You will also use functions to group tasks like addition into reusable blocks. The goal is to create a program that responds to commands, performs calculations, and can grow with your skills. When you finish, you will have a working calculator and a strong understanding of C++ basics.

Control structures are essential for interactive programs. In your calculator, they allow it to respond to user input instantly. Without them, your program would be a fixed script, unable to handle choices like “add” or “subtract” or repeat calculations—features critical for real software.

Functions are vital for organizing your code efficiently. In this calculator, they keep operations separate and reusable, preventing a cluttered mess. They also make your program scalable; adding new features like multiplication becomes simpler with functions. Together, control structures and functions help you build effective software, starting with this calculator.

info> Note that, should you get stuck at any time, there is a solution folder that contains the full code solution for this lab!

In this step you will explore basic control structures that will prop up the logic of your calculator. These control structures will make your calculator respond to user input and repeat tasks. This step focuses on using if-else statements and loops to manage basic program flow and set up the calculator’s menu system. These skills are important for adapting to user choices and running multiple calculations. Your calculator needs to let users choose operations like addition or subtraction. Using if-else statements of the form:

  if (choice == 'a') {
	
	} else {
	
	}

allow you to process input and take action, forming the foundation for a responsive program. When your calculator has more operations, many if-else statements can become hard to read. A switch statement offers a clearer way to handle specific choices, making your code easier to maintain and expand. Switch statements generally look like this:

switch(value) {
  case('a'): {
    // Do work
    break;
  }
	// more case statements as needed
 default: 
   // Default fall-through
}
``` Users expect a calculator to handle multiple calculations in one session. A `for` loop enables this repetition, preparing your program to manage several inputs effectively. This is what a `for` loop with three iterations looks like:

```c++
for (int i = 1; i <= 3; i++) {
  // Body of the for loop
}

Now you will enhance your calculator with advanced control structures. Nested conditionals and loops with conditions will improve input validation and program flow, making it more reliable. Out in the real world, not many programs and applications are very simple. Sometimes you need to only loop when a certain condition is met or check for nested boolean conditionals. This is when more advanced control structures come into play. In this step, you will continue to improve your calculator by adding nested conditionals, break statements, and a while loop. Users may enter incorrect data, such as invalid numbers, and your calculator must manage this without failing. Nested if statements allow you to add extra checks, ensuring your program remains stable. A calculator needs an exit option so users can stop when finished. Using the break keyword will let you break early out of control structures like loops and switch statements. The break keyword is especially critical for switch statements where they delineate the true ending of a switch case. Your calculator should continuously run in the background - prompting the user for input. This can be achieved via a while loop. The while loop is like a for loop but instead of a fixed number of iterations, a while loop will loop until a certain condition is met (or not met). Here is an example of a while loop:

while(true) {
 // This loop will run forever
}

Next, you will use functions to organize your calculator’s operations. This step focuses on creating functions for arithmetic tasks, keeping your code modular and manageable. Functions are critical for reusing code efficiently, like separate calculator buttons.

In C++ functions are comprised of 3 parts:

• The return type: this is the portion of the function that specifies what the function returns

• The signature: this is that part of the function that contains the function parameter list and their associated types.

• The body: the body of the function, enclosed in curly braces, is where the actual encapsulated logic of your function resides.

Here is an example of an add function in its three parts:

• Return type: double

• Signature: `add(double a, doubleb)

• Body:

{ 
  return a + b; 
} 

Putting these 3 parts together gives you a function declaration in C++. To then call your function, you then just specify the function name along with parenthesis and the function arguments like this: add(1, 2).

Functions are a key part of not just C++ programming, but programming in general as it is the primary means by which you can define reusable bits of logic! Addition is a core calculator operation. Writing it as a function lets you reuse it anywhere, reducing repetition and keeping your code clean - an important practice in software development. Subtraction is another key operation. Creating a separate function for it keeps your code organized and makes it easier to fix or change later, improving maintainability. Your calculator must use user choices to perform calculations. Connecting functions to those choices links your control structures to the operations, making your program functional.

Good job—you have built a command-line calculator with control structures and functions in C++! You have completed a practical project that shows your ability to manage program flow and organize code effectively. This lab has given you valuable skills you can use in many programming tasks.

You have learned how to use control structures to direct your program’s behavior. With if-else and switch statements, you handled user choices, such as selecting addition or subtraction, and validated inputs to keep your calculator running smoothly. Loops like for and while allowed you to repeat tasks—whether collecting multiple numbers or prompting until valid input was received. These skills help you create programs that respond to users and handle real-world scenarios.

You have also mastered functions to structure your code. By writing add() and subtract(), you made operations reusable and kept your program modular. This approach is essential for building larger projects without losing control of your codebase.

Now, consider your next steps to improve this calculator. You could add more operations, such as multiplication and division, by defining new functions and updating your menu and switch statement - your current structure makes this straightforward. Another option is to track previous calculations with a history feature, using an array to store results and a function to display them. If you want a challenge, try handling division-by-zero errors with additional validation.

Feel free to check out more C++ video courses and code labs here at Pluralsight!