Modular Programming

1
Modular Programming

• From Chapter 6

2
Output Parameters

• Pass by reference.
• In the calling program
• int frog, lily
• int frog_ptrfrog
• function_name(frog_ptr, lily)
• In the called function
• function_name(int fp, int ly)
• fp 12
• ly 15

Two different ways.
3
Pre and Post Conditions

• An excellent design technique.
• Described first in chapter 3 (pg 131)
• Precondition
• A condition assumed to be true before a function
  call.
• Postcondition
• A condition assumed to be true after a function
  call.
• Normally written in English and verified after
  the function is written.

4
Introduction to Scope

• Another word for scope is visibility.
• define variables scope begins at their
  definition and ends at the end of the source
  file. All functions can see these variables.
• The scope of the name of a function begins with
  the function prototype and ends with the end of
  the source file.

5
Scope (cont.)

• All formal parameter names and local variables
  are visible only from their declarations to the
  closing brace of the function in which they are
  declared.
• Look at Fig 6.8 and pay particular attention to
  Table 6.4 until you agree with ALL the
  visibilities.

6
Scop (cont.)

• If you use prototypes correctly, and watch what
  names you use for functions, and formal
  parameters, you shouldnt have scope problems.

7
Passing output parameters on

• Since a formal output parameter is an address
  already, if you pass it on to a scanf, you dont
  need the operator.
• Calling program
• c funct(a, b)
• In the called program
• int funct(int fa, int fb)
• int lc
• scanf(, fa, lc, fb)

8
Case Study (6.5)

• If you are a bit shaky with top-down design and
  implementation, review this case study carefully.
• Problem
• Analysis
• Data Requirements
• Design
• Initial algorithm
• Refinements
• Implementation
• Testing

9
Case Study (cont.)

• Also review the structure chart in figure 6.11.
• Very helpful in keeping track of the design
  youre implementing.

10
Debugging

• Driver
• A short version of code used to call a specific
  function. It replaces the code above the
  function in the structure chart.
• Stub
• A short version of code used to replace the
  called functions by a specific function. It
  replaces the code below the function in the
  structure chart.

11
Top Down and Bottom Up

• Top down doesnt need drivers, just use the real
  code.
• Bottom up doesnt need stubs, just use the real
  code.

12
Intermediate Makefiles
Makefile using variables OBJS rut1.o
fun1.o CC gcc DEBUG_FLAGS -g rut1
(OBJS) (CC) (DEBUG_FLAGS) o rut1
(OBJS) rut1.o rut1.c proto.h (CC)
(DEBUG_FLAGS) c rut1.c fun1.o fun1.c
proto.h (CC) (DEBUG_FLAGS) c
fun1.c clean rm rut1 .o
13
A comment about printf

• If too many expressions are supplied in the
  printf statement, the extra ones will be ignored.
• printf(d d\n, 1, 2, 3)
• If there are not enough expressions, C will
  generate strange numbers for the missing
  expressions.
• printf(d d d \n, 1, 2 )

1 2
1 2 134513293
14
Additional Special Characters

• \b Backspace
• \f Form Feed
• \n New Line
• \r Return
• \t Tab

• \ Apostrophe
• \ Double Quote
• \\ Back Slash
• \nnn Character number nnn (octal)