3.12 Calling Procedures

Every morning you brush your teeth, wash your face, and eat breakfast. You don’t rewrite those steps every day — you just do them. That’s what calling a procedure is: you already have the steps (the function), and you just call it whenever you need it.

What is it?

  • A procedure is a reusable group of instructions.
  • Also called a function in Python or JavaScript.
  • Procedures allow you to avoid rewriting the same code. What does it mean?
  • Calling a procedure means telling the computer to run the instructions in that procedure.
  • You can call a procedure multiple times with different input values without rewriting it.
  • This is different from defining the procedure — defining is creating it, calling is using it.

Python Example:

  • Use def to define a procedure
  • You can use the name of the functionand paranthesis after to call it
# Define a procedure
def show_message():
    print("Welcome to the program!")

# Call the procedure
show_message()  # Output: Welcome to the program!

Welcome to the program!

Javascript Example:

  • You use function to define a procedure
  • Just like python if you type the name of the function with parenthesis right after it, you can call the procedure
// Define a procedure
function showMessage() {
    console.log("Welcome to the program!");
}

// Call the procedure
showMessage();  // Output: Welcome to the program!

Calling A Procedure Inside Another Procedure

Why?

  • Large problems can often be broken into smaller steps (decomposition).
  • Each step can be a procedure, and one procedure can call another.
  • This makes programs easier to read, debug, and reuse.

Python Example:

  • Calling the procedure format_name returns the formatted name so the other procedure can use it
def format_name(first, last):
    return first + " " + last

def greet_person(first, last):
    full_name = format_name(first, last)
    print("Hello, " + full_name + "!")

greet_person("Sathwik", "Kintada")  # Output: Hello, Sathwik Kintada!


Hello, Sathwik Kintada!

JavaScript Example:

  • Calling the procedure formatName returns the formatted name so the other procedure can use it
function formatName(first, last) {
    return first + " " + last;
}

function greetPerson(first, last) {
    let fullName = formatName(first, last);
    console.log("Hello, " + fullName + "!");
}

greetPerson("Lucas", "Masterson"); // Output: Hello, Lucas Masterson!

<IPython.core.display.Javascript object>

Key Takeaways

  • Helper procedures do one simple task.
  • Outer procedures call helpers to combine or display results.
  • This is decomposition — breaking a problem into smaller steps.
  • Calling procedures inside procedures makes code reusable and organized.