Calling Procedures Chapter Notes | AP Computer Science Principles - Grade 9 PDF Download

Introduction

Calling procedures is a key concept in AP Computer Science Principles, allowing programmers to reuse sets of instructions efficiently. This chapter explains what procedures are, how they are defined, and how they are used in programs. It covers the role of parameters and arguments, as well as how to return values from procedures. By understanding procedures, programmers can write cleaner, more organized code without repeating the same instructions multiple times.

Procedures and Procedure Calls

• A procedure is a group of programming instructions that can be reused, also called a function or method in some languages.
• Procedures let you use the same code multiple times without rewriting it.
• In AP Pseudocode:
  • Define a procedure: PROCEDURE procName(parameter1, parameter2, ...) { block of statements }
  • Call a procedure: procName(arg1, arg2, ...), where arguments (arg1, arg2) are assigned to parameters.
  • The procedure can take zero or more parameters.

Parts of a Procedure

• Parameters are input variables that a procedure uses to perform its task.
• Example: A procedure to add two numbers needs two parameters (e.g., first_number, second_number).
• Not all procedures require parameters.
• Arguments are the actual values or variables passed to a procedure when it’s called.
• In Python:
  • Define a function: def name_of_function(parameter1, parameter2): # code statements
  • Example: def summing_machine(first_number, second_number): print(first_number + second_number)
  • Call with arguments: summing_machine(5, 7) outputs 12.
• When a procedure is called, the program executes its code as if it were written in place, then continues with the next line of code.

Return Statement

• A return statement lets a procedure send a value back to the code that called it.
• In AP Pseudocode:
  • PROCEDURE procName(parameter1, parameter2, ...) { block of statements; RETURN expression }
  • The RETURN statement stops the procedure and returns the value of the expression.
  • Assign the returned value: result ← procName(arg1, arg2, ...)
• In Python:
  • Example: def summing_machine(first_number, second_number): value = first_number + second_number; return value
  • Call and assign: answer = summing_machine(5, 7); print(answer) outputs 12.
  • Use the returned value: print(answer + 1) outputs 13.
• The return statement can appear anywhere in the procedure and exits it immediately.

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Key Terms

• Arguments: Values provided to a function when it is called, allowing customization of the function’s behavior.
• Parameters: Variables defined in a function’s declaration that act as placeholders for the arguments passed during a call.
• Return Statement: A statement that specifies the value a function should send back to the calling code, enabling further use of the result.