# Mastering Python Basics: Build a Command-Line Calculator Program

## Introduction to Command-Line Calculator Program

Computers are commonly perceived as highly complex machines, but the truth is that they have a simple logic that we can tap into. The command-line interface is one of the most used environments for completing a wide variety of tasks, which includes creating simple calculator programs.

In this article, we will be discussing how to create a command-line calculator program that can execute mathematical operations. We will be focusing on the two critical aspects of creating a command-line calculator program, accepting input from the user and creating the mathematical logic to calculate the result of the equation.

### Accepting/Prompting User Input

The first step in building any calculator program is to accept user input. However, receiving input in a script is different from the way we input numbers in a typical calculator.

In Python or any other programming language, we use the `input()` function to receive data entered by the user. The function accepts a string argument, which provides a message to the user requesting the input value.

Here is an example of how to use the `input()` function in Python to prompt the user to input two numbers:

``````num1 = input("Enter the First Number: ")
num2 = input("Enter the Second Number: ")``````

In this example, you can see that the `input()` function is used to take user input. When the program is executed, two prompts will appear on the screen asking the user to enter the first and second numbers.

Once the user inputs the values, they will be stored in the variables `num1` and `num2`, respectively.

## Operators and Output Formatting

The next step is to include the mathematical operations that the calculator program will execute. The four primary mathematical operators are addition, subtraction, multiplication, and division.

These operators are represented by some symbols on a calculator. To use these symbols in our script, we represent them as follows:

• Subtraction – –
• Multiplication – *
• Division – /

In Python, we can run mathematical operations using these mathematical symbols. In the case of our calculator program, we can use the user input values to generate the output using the desired operator.

### Here is an example of a Python script that can add two numbers entered by the user:

``````def add(num1, num2):
return num1 + num2

In this code, we create a function `add()` that takes two arguments `num1` and `num2`. The function then performs the addition operation on the arguments and returns the result.

We then print the result using the `print()` function. The output for this code snippet will be:

``Result: 8``

This code is a simple example of how we can use Python programming language to create a calculator program.

Similarly, you can create functions for other mathematical operations and use them accordingly. One thing to note while printing the result of a mathematical operation is the output formatting.

You can format the output using the built-in `format()` function. Here is an example of how to include output formatting:

``print("Result: {0:.2f}".format(3.1415))``

Output: Result: 3.14

In this example, we have used the `format()` function to print the output with two decimal places.

The output would have been 3.1415 if we hadn’t formatted it using the method shown above.

## User-Choice Based Calculator Program

### Including Conditional Statements

Our calculator program becomes more versatile and intuitive when we allow users to choose which mathematical operator they want to use when they want to carry out the calculation. For this purpose, we will have to use conditional statements.

In programming languages such as Python, we can use `if-else` loops to create conditional statements. Here is an example code that checks whether the entered values for the two variables are numbers:

``````num1 = input("Enter the First Number: ")
num2 = input("Enter the Second Number: ")

if num1.isnumeric() and num2.isnumeric():
num1 = float(num1)
num2 = float(num2)
else:
print("Invalid Input")``````

In this code example, we use the Python function `isnumeric()` to check whether the user input is a number.

If both values are numbers, we then convert the string input to floats using the `float()` function. If either of the input values is not numeric, the program outputs an error message.

### User Input Validation

In addition to checking whether an input is a valid number, we need to ensure that the selected operator is valid as well. We can use the same conditionals mentioned earlier to check whether a valid operator is selected.

Here’s an example of implementing user input validation:

``````num1 = input("Enter the First Number: ")
num2 = input("Enter the Second Number: ")
operator = input("Select the Operator (+, -, *, /): ")

if num1.isnumeric() and num2.isnumeric():
num1 = float(num1)
num2 = float(num2)
else:
print("Invalid Input")

if (operator == "+"):
print("Result: ", num1 + num2)
elif (operator == "-"):
print("Result: ", num1 - num2)
elif (operator == "*"):
print("Result: ", num1 * num2)
elif (operator == "/"):
print("Result: ", num1 / num2)
else:
print("Invalid Operator Selected!")``````

In the code example, we include an “if-else” loop that matches the input operator to a valid operator. If it matches, the corresponding calculation is executed and printed on the command line.

If the operator input does not match any of the four valid operators, an appropriate error message is displayed.

## Conclusion

In conclusion, building a command-line calculator program is a great way to learn programming basics and practice using some of the core concepts and syntax in Python. In this article, we covered two critical components of creating a command-line calculator program: accepting user input and creating mathematical logic to solve equations.

Moreover, we discussed how to use conditional statements and validate user inputs to create a versatile calculator program. With a little bit of time and practice, it is possible to build more complex calculator programs and integrate additional functionality that is tailored to your requirements.

## 3) Prerequisites for Setting up the Program

Before you can create your command-line calculator program in Python, you need to ensure that certain prerequisites are met. Here are the two essential prerequisites that you need to have in place to start building your program:

### Python 3 Installation

The first step to creating a command-line calculator program is to have Python 3 installed on your computer. Python is a free and open-source programming language that can be downloaded and installed on Windows, Mac, and Linux.

To install Python 3, you can visit the official Python website and select the version that is compatible with your operating system. Once the download is complete, follow the installation instructions to install Python 3 on your computer.

### Programming Environment Setup

After installing Python 3, the second essential step is setting up your programming environment. A programming environment comprises a code editor, a compiler, and a debugger, which allow you to write, test, and debug your Python code.

There are several programming environments available for Python developers. Here is how you can set up a programming environment using two of the most popular code editors:

• Visual Studio Code: After installing Python 3 on your computer, you can download and install Visual Studio Code, which is a free code editor.
• Once installed, launch Visual Studio Code and install the “Python” extension from the Visual Studio Marketplace. You can now create a new Python file and start writing your command-line calculator program.

• PyCharm: PyCharm is a popular code editor developed by JetBrains, which is specially designed for Python developers. After installing Python 3, you can download and install PyCharm Community, which is a free version of PyCharm.
• Once installed, you can create a new Python file and start writing your command-line calculator program.

## Conclusion and References

In conclusion, building a command-line calculator program is a simple yet effective way for beginners to learn the basics of Python programming.

In this article, we covered the essential components required to create a command-line calculator program, such as accepting user input and mathematical logic for calculating equations. We also covered the prerequisites required, including installing Python 3 and setting up a programming environment.

To further enhance your Python knowledge and skills, here are some additional references that you can use to deepen your understanding:

• Python documentation: The official Python documentation is a comprehensive resource for learning the Python language. It covers all the details of Python, from basic concepts to advanced features.
• Python tutorials: There is a vast collection of tutorials available for learning Python on various online platforms, including YouTube, Udemy, and Coursera.
• Python books: There are many Python books written by experts that cover all aspects of the programming language.

Some of the most popular Python books include “Python Crash Course” by Eric Matthes and “Learning Python” by Mark Lutz. By referring to these resources and practicing your programming skills, you can master Python and create more advanced applications.

In conclusion, creating a command-line calculator program in Python is an excellent way to learn programming basics and implement core concepts such as accepting user input and generating mathematical logic. To create this program, you need to ensure that the essential prerequisites are met, such as installing Python 3 and setting up a programming environment.

This article covered all the key points, including prompting user input, operators, output formatting, conditional statements, and user input validation. The article also provided references for further reading to deepen your understanding of Python.

By practicing your programming skills and building more complex calculator programs, you can enhance your Python knowledge and advance your career as a programmer.