Chapter 3
Top-Down Design with
Functions
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Objectives
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Building Programs from Existing functions
Some Mathematical Library Functions
Create you own functions
Top-Down Design & Structure Charts
Declare Functions
Order of Execution of Function
Subprograms and Main function
The Function Data Area
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Building Programs from Existing
Information
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Programmer seldom start off with an empty program
Reasons:
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Most basic or frequently used functions have been written by
other programmers
If you write every function by yourself, the source code may be
messy and hard to maintain
Less code, less bugs
Deadline
Many existing libraries have tuned the performance, and are
more reliable and robust.
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Conversion Program
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We have used some pre-written I/O functions
provided in C
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Predefined Functions and
Code Reuse
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A primary goal of software engineering is to
write error-free code.
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C library functions provide most commonly
used functions.
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Code reuse: reusing program fragments that have
been written and tested.
e.g., mathematical library <math.h>
To use existing C library functions, we have to
include the header file of the corresponding
library.
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e.g., #include <math.h>
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Square Root computation
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Square Root Program
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Square Root Program (cont’d)
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Some Mathematical Library
Functions
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Your own functions?
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Top-Down Design & Structure
Charts
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Most likely a problem is complex, and we have
to break up the problem into subproblems.
Top-Down Design is a method in which we
break a problem into subproblems, and derive
the solution for the original problem.
Structure Chart is a documentation tool that
shows the relationships among the subproblems
of a problem.
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Example: Draw Simple Diagrams
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House and Female Stick Figure
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House and Female Stick Figure
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The house consists of a triangle without its
base and a rectangle.
The female stick figure consists of a circle, a
triangle, and a triangle without its base.
Suppose we are given four basic drawing
components (functions).
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A circle
Parallel lines
A base line
Intersecting lines
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Structure Chart
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Use and define your own
functions
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One way to implement top-down design
is by defining your own functions.
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Usually a subproblem is solved by a
corresponding subproblem.
Functions without Arguments
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Simple Functions that have no arguments
and return no value.
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Declare Functions without
Arguments
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Declaration: ftype fname(void);
The identifier ftype specifies the data
type of the function results.
Example: void fname(void);
After fname() is called, the execution of
the program jumps to the subprogram
defined by fname.
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Example: Function Prototypes &
Main function for Stick Figure
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Function Definitions
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Order of Execution of Function
Subprograms and Main function
1.
2.
3.
When the computer executes a function call statement, it
transfers the control to the function.
The computer allocates memory for variables used in the function
and executes the statements in the function body.
After the execution of the function, the control is returned to the
calling function and the allocated memory is released.
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Advantages of Using Function
Subprograms
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Procedural Abstraction
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The main function consists of a sequence of function
calls.
We defer implementation details until we are ready to
write the subprogram.
We can focus on one function at a time.
Reuse of Function Subprograms
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The subprogram can be executed more than once in
a program
Decrease the length of code and chance of error.
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Function with Arguments
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The arguments of a function are used to
transfer information between the calling and
called functions.
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Input Arguments are used to pass information
into a subprogram from the calling function. (in
this chapter)
Output Arguments are used to return results to
the calling function. (in Chap 6)
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Void Functions with Input Arguments
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We can create functions that receive input
arguments but do not return any results.
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Functions with Input Arguments
and A Single Result.
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Example: Single Input &
Single Output
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Effect of Executing
circum = find_circum (radius);
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Example: Multiple Input
Arguments & Single Output
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Function scale multiples the first input argument
by 10 raised to the power indicated by the second
input argument.
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The Function Data Area
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The Function Data Area
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Homework #3
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Programming Project 4 (Textbook. Page 141)
due: 2006/10/11
讓使用者輸入一個物體發射的仰角、初速、目標所在的距離
將下列兩個計算寫成兩個function
並印出你的計算結果
1. 此物體到達目標的時間
time 
dis tan ce
velocity * cos( )
2. 此物體到達目標時離地面的高度
g * time2
height  velocity * sin(  ) * time 
2
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Summary
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Building Programs from Existing functions
Some Mathematical Library Functions
Create you own functions
Top-Down Design & Structure Charts
Declare Functions
Order of Execution of Function Subprograms
and Main function
The Function Data Area
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