Exam Homework

1
Exam / Homework

• Exam 1
• Solutions Posted
• Questions?
• Starting KR chapter 4 tonight
• Read Glass and Ables Section on MAKE
• Start on HW4 - Due Class 13

2
Functions and C Program Structure

• C makes functions efficient and easy to use
• Program ! a few big functions
• Program many small functions
• Functions may reside in separate source files
• Source files compiled and loaded separately
• An Introduction to MAKEFILE is coming (A process
  that KR does not go into)

3
C Program File Structure

• In file main.c
• / function prototypes /
• include function.h / indirect /
• int foobar(int, float) / directly /
• int main()
• int n foobar(function(), 1.0)
• int foobar(int i, float j)
• / statements using i and j /
• return (some integer expression)

4
C Program File Structure

• In file function.h
• / function.h function prototype /
• int function(void)
• In file function.c
• / function.c function code /
• include function.h
• int function()
• / function code /

5
Function Prototypes

• Special case for null argument lists
• Always code function prototype as
• int foo (void)
• Keeps compiler parameter checking enabled
• Demonstration of bad example
• int foo ()
• x foo (i, j, k) / compiler wont catch! /

6
Post-fix Notation

• For hw4, you need to know how to convert an
  algebraic (in-fix) expression to post-fix
• Some calculators work this way, e.g H-P
• Algebraic (123 21) (567 432)
• Post-fix 123 21 567 432 -
• No parentheses are needed!
• Hows that work?

7
Post-fix Implementation with a Stack

• Enter 123 21 567 432
  -
• Stack
• States

123
21
144
567
432
135
19440
Empty
123
144
567
144
144
8
Post-fix Calculator Program

• Pseudo-code for In-fix calculator (See KR, pg
  75)
• while (next the character is not an EOF)
• if (number)
• push it on the stack
• else if (operator)
• pop operand(s) / may be one or two /
• do operation
• push result back on the stack
• else if (newline)
• pop and print value from top of stack
• else error

9
Post-fix Calculator Program

• See KR, page 76 and then page 78
• Operand order is not important for some ops
• , , ,
• Operand order is important for some ops!
• -, /,
• There is only one operand for some ops
• , !,

10
Post-fix Calculator Program

• Break down the pseudo-code into functions
• push / pop
• get next number or operator, i.e. get op ( )
• getch / ungetch
• Both push and pop access a set of variables for
  the stack ? static external
• Both getch and ungetch access a buffer for
  characters from stdin ? static external

11
Communication Between Functions

• Sometimes closely related functions need to share
  access to variables in situations where they
  never call each other and therefore cant pass
  arguments to the shared variables
• Ex push and pop share the stack variables
• Declare static variables inside source file for
  the functions (before / outside the braces for
  any of the functions) ? Static External per KR
• Makes them globally accessible to all functions
  in the source file (similar to Java class
  variables)

12
Multi-Module ProgramsGlass Ables, pg 397(3 ed.)

• To compile all .c files and create executable
• gcc main.c getop.c stack.c getch.c o calcit
• To compile only one and create executable with
  objects of previously compiled files
• gcc main.c getop.o stack.o getch.o o calcit
• To build an executable from a complex set of
  separate files skipping any unneeded steps
• make f makefile (makefile documents build rules)

13
Dependency Tree for a Build
calcit
main.o
getop.o
stack.o
getch.o
main.c
getop.c
stack.c
getch.c
getop.h
stack.h
getch.h
14
Make (Glass, pg 347)

• makefile rule format
• target dependency list for needed files
• command list to create target
• Example
• calcit main.o getop.o stack.o getch.o
• gcc main.o getch.o -o calcit
• Note Must use tabs to indent not spaces

15
Make

• CC is defined early in the makefile with the
  line
• CC gcc
• Then using (CC) causes substitution
• calcit main.o getop.o stack.o getch.o
• (CC) main.o getop.o stack.o
  getch.o -o calcit

16
Make

• The user can type the command "make", or make
  with a named target, for example
• make getop.o to cause the rules leading up to
  the target getop.o to be executed, if needed.
• When user types "make" without a target name, the
  FIRST rule listed will be the default target
  constructed. Thus, the "calcit" rule should be
  the first rule in the makefile

17
Make

• At the end of the makefile, there is a rule with
  a target name "clean".
• clean
• rm .o
• Since "clean" is not a file
• There is no dependency list (ages of files don't
  matter)
• It is called when you give the command "make
  clean".
• It deletes .o files to reduce the clutter in the
  directory.

18
Header Files

• Principles for contents of .h files
• Each .h file includes all of the function
  prototypes and symbolic constants needed to
  invoke those functions
• int function (int ) / no code for function
  /
• define VALUE0_FOR_ARGUMENT 0
• No statements that allocate memory in .h files!!
• Dont use a single calc.h file (KR, pg 82)
• A reusable solution shown in Dependency Tree
• An xxx.h file for each xxx.c source file of
  functions
• include getop.h in getop.c and all source files
  that call functions provided in the getop.c
  source file (i.e. main)

19
Header Files Math Library

• When you want to use math functions
• Example SIN( ) or SQRT( )
• Write
• include ltmath.hgt
• But also invoke compiler with special flag
• gcc -lm . . . (lm means library, math)

20
Back to Post-fix Calculator Program

• Look at getop, getch, ungetch functions
• In getop( ), we try to input a char string for a
  number. But if the string ends with a '', we
  want to put that back in stdin, somehow, for a
  successive invocation of getch
• We do this with ungetch( )

21
getch.c

• define BUFSIZE 100
• static char bufBUFSIZE / buffer for ungetch
  /
• static int bufp 0 / next free position in
  buf /
• / get a possibly pushed back char from stdin /
• int getch(void)
• return (bufp gt 0) ? buf--bufp getchar( )

22
getch.c

• / push char back for getch later /
• void ungetch(int c)
• if (bufp gt BUFSIZE)
• printf("ungetch too many characters in
  buffer.\n")
• else
• bufbufp c