## Pages

### Problem Solving With Python: Program 0

The problem statement:

The task is to write a Python program that displays a list of numbers from 4 to 9. Next to each number, the program will also display its square. The square of a number is computed by multiplying it with itself like so. 4 x 4 = 16. Here, 16 is the square of 4.

The following is the expected approximate output of program 0:

4 16
5 25
6 36
7 49
8 64
9 81

The Solution:

``def program_0():    number = 4    print(number, number * number)    number = 5    print(number, number * number)    number = 6    print(number, number * number)    number = 7    print(number, number * number)    number = 8    print(number, number * number)    number = 9    print(number, number * number)if __name__ == '__main__':    program_0()``

How do I setup?

Follow the steps at this link to get started. When following the instructions assume that your machine does not already have Python installed so that you follow the instructions for downloading Python and making sure you install version 3.10. Ignore the details of the program in this example and instead focus on running the program in their example.

How do I run the program?

Running the code. If you followed the steps from the setup section than you should now how to create a file and run a Python program in Python. In your python project create a module (file) called program_0.py. Type the code in this file as shown and run the program. If your setup was successful then the Python interpreter should have run your program that generates some output within PyCharm.

What is a code interpreter?

The Python Interpreter is a program that reads and execute Python code. In order for the interpreter to be able to do its job, the program that we write must follow a set of rules. Code indentation is one of these rules. Violation if this or any programming rules will result in a program that does not execute or, even worse, a program that executes incorrectly.

What is a variable?

A variable is a name for a physical location within the computer that can reference either a single piece of data like a number or a character or data structures that can hold multiple pieces of data. In our program we define the variable number that holds a single number. As the name implies, a variable can be changes by our program as it is running. Our program first defines this variable number by assigning the number 4 to it. Our program then changes the value that our variable is referencing with the use of the assignment operator.

Why use a variable at all?

Variables will allow us to write code that is concise, descriptive and reusable. The importance of these ideas will become more evident as we write programs with increasing complexity.

What is an assignment operator?

The assignment operator, denoted by =, is used to assign a value to variables. The following is a general form of an Assignment Statement.

``variable_name = expression``

What are Python Keywords?

Python keywords are reserved words that should not be used except for its explicitly defined usage. The keywords used in this program are the following.

1. def is used to define the start of a function.
2. if is used to test a condition. In our case it is used to test if the variable __name__ is equal to the string __main__. If it is then the next indented lines are executed by the interpreter. In our case, our function, program_0() is executed, resulting in an output that is generated by our program.

What is a function?

A function is a building block of a program; they are used to define code that is reusable and can be called anywhere within your program. Note how we first write our display logic in def program_0()... then further down we call it. Suppose we wanted to display the same values again immediately below the first program output. This can be accomplished in one of two ways. We can either modify our program to display the values twice or simply call our program immediately following the first call like so.

``if __name__ == '__main__':    program_0()    program_0()``

Hence, code reuse!

What is a built-in function?

Python is shipped with many standard built in functions. Our program the built-in print(...) function to display our values to the monitor. We can pass any number of variables to the print function with the use of a comma. The print function will display the variables passed to it by inserting a single space between them. The print function will also add to the end a newline character so that the display system will print the next values on a new line.

Page with links to the entire series can be found here

Are you having any issues running or understanding the program? Please, add a comment explaining where you are stuck or where the tutorial is not clear so we can improve it.