Class 23: Functions and Parameters

Held: Wednesday, 2 March 2011

Summary: We consider some issues with functions in C.

Related Pages:

• EBoard.
• Lab: Basic Functions in C.
• Reading: K&R 4.1-4.3.
• Due: Assignment 5.

Notes:

• I'll reserve time at the start of class for questions on Assignment 5.
• When you're in a group and email me a question, it's nice if you carbon-copy your colleagues so that I can just hit reply-all.
• Assignment 6 should be ready some time on Thursday. I'll email you when it's ready.
• I've posted some answers to your questions on the control flow reading.
• Questions on reading missing from: DF.
• Next reading: K&R 4.3-4.6.
• EC: Thursday's CS Extra: FPGAs.
• EC: Friday's CS Table: GPU programming in CUDA, revisited.

Overview:

• Basics of functions in C.
• Compiling.
• RPN and Stacks.
• Lab.

Functions in C

• The form of a procedure definition

  TYPE
  NAME (PARAMETERS)
  {
    BODY;
  } 
  

• Problem: How does the C compiler know if you're using a procedure in the correct way?
• Solution: Declarations, which appear at the top of your program
• Form of declarations:

  TYPE NAME (PARAMETERS);
  

The Compilation Process

• The computer spends some effort going from human-readable programs (e.g., written in C) to computer-readable programs.
• For the C compiler, the process is as follows:
• First, preprocess the code (cc -E)
  • Load included files
  • Strip out comments
  • Resolve #defines
• Next, translate the code into assembly language (cc -S)
  • Assembly is a semi-human-readable version of the underlying computer code.
• Next, assemble the assembly code into object code (cc -c)
  • Object is computer-readable code that needs a few tweaks to be executed.
• Finally, link the various object files together into an executable.

Stacks and Reverse-Polish Notation

• RPN: An unambiguous way of computing that doesn't require parentheses.
  • Write the operator after the operands.
• Easy to implement
  • When you see a value, add it to the end of a list of things to process.
  • When you see an operator, grab the last two things on the list apply the operator, and add the result back to the end of the list.
• Stack: An ADT that supports those two operations (plus a few others).
  • Basically, stacks are collections of values that implement that last in, first out principle.
  • Add to the stack is called push
  • Remove from the stack is called pop

Lab

• Do The lab.
• Be prepared to reflect.