Programming Chapter 6: Subprograms

Chapter 6: Subprograms

• Subprograms are self-contained blocks of code
• Subprograms have a single entry point
• Execution of the calling program is suspended whilst the subprogram runs
• Control returns to the caller when the subprogram's execution finishes

Subprogram General Form

• subprogram_type subprogram_name(parameter_list)
• { body of the subprogram }
• subprogram_type: specifies the subprogram type
• subprogram_name: a valid identifier
• parameter_list: variables receiving values upon calling

Parameters

• Formal parameters are dummy variables within the subprogram header
• Parameters in a call statement are 'actual' parameters, which are bound to formal parameters
• Subprogram call statements need the subprogram name and a list of actual parameters matching formal parameters

Parameter Modes

• in: parameter can only be read, not written
• out: parameter is written to and then read, potentially changed after the subprogram
• in out: parameter can be both read and written to, potentially changing

Models of Parameter Passing

• Diagrams illustrate 'in', 'out', and 'inout' modes as different data flow between calling and called programs
• Diagrams visually represent parameter passing within subprograms

Pass-by-Value (In Mode)

• The actual parameter's value initializes the formal parameter
• Usually implemented by copying the value
• Can be implemented by transmitting an access path instead of copying but is less efficient
• Disadvantages involve extra storage if the physical move approach is used, particularly for large parameters

Pass-by-Result (Out Mode)

• Requires extra storage space
• A copy operation is necessary to update the value of the caller's parameter after the subprogram step

Pass-by-Value-Result (Inout Mode)

• A hybrid of pass-by-value and pass-by-result methods
• Sometimes called pass-by-copy
• Formal parameters often have local storage for this method

Types of Subprograms

• Two main categories: Procedures and Functions
• Procedures: sets of statements that create parameterized computations
• Functions: semantically similar to procedures, but modeled on mathematical functions

Sample Procedure

• Example procedure Sumit
• Displays the structure of a procedure, Sumit with an in parameter and an out parameter.
• Shows a for loop computing a sum

Sample Function

• Example function Sumit
• Illustrates a function with an in parameter (e.g., integer N) and a defined return type (e.g., integer).
• Shows a for loop computing a sum, returning a calculated value.

This quiz covers the concepts of subprograms in programming, focusing on their structure, parameters, and modes of operation. You will learn about the significance of self-contained blocks of code and how parameters function within subprograms. Test your knowledge on the general form of subprograms and their execution.