COMP104 Special Tutorial

1
COMP104 Special Tutorial

• 22 SEPT 2005

2
Outlines

• Real and Programming Environment
• A C Program
• Write a Program - HOWTO
• Divide-and-conquer
• Understand the requirements
• Analyze the logic
• Implement your program
• Test your program
• Good Practices
• Example

3
Real and Programming Environment

• Programming environment is NOT the same as the
  real environment
• Share some similarity and dissimilarity
• C program is constructed from basic types (int,
  char, etc)
• gttry to map the input/output/operations to them
• Conditional and repetition statements
• ifelse, switch
• for, while, dowhile

4
Real and Programming Environment

• How to solve daily life problems with
  programming?
• Knowledge of data types (primitive types, class,
  struct, etc). Do you know how to convert the
  daily life input and output to C data types?
• Understanding of different syntaxes (looping,
  conditional, etc) available. Could you point out
  some similar scenarios in daily life?
• Practice, practice and practice. The skills can
  only be improved by writing your codes and
  reading more examples.

5
A C Program

• Generally speaking, the source code can be
  divided into functional and non-functional
  portions
• Functional (What should the program perform?)
• Logic details (including logic design)
• Non-functional (No effect on the program
  functionalities but improve the readability)
• Indentation
• Spacing
• Comments

6
A C Program
Libraries to be included (functions, constants,
etc)
main function (your program logic)
// A typical C program include
ltiostreamgt using namespace std int main() //
variable and constant declaration const int
MAX_NUM_INPUT 8 char userInput // prompt
user for a character cout ltlt "Enter a character
" cin gtgt userInput // display the user
input cout ltlt "You have typed \'" ltlt userInput
ltlt "\'!" ltlt endl return 0
Comments
Indentation
7
Write a Program HOWTODivide-and-conquer

• A single problem is too large to be solved
• Divide the problem to sub-problems until you
  could find a solution for it (conquer)
• You will learn C functions later
• Example
• Write a program to compute and output the mean,
  maximum and minimum scores from a set of scores
• Input the scores
• Compute the mean score
• Compute the maximum score
• Compute the minimum score
• Display the mean, maximum, minimum scores

8
Write a Program HOWTOUnderstand the
requirements

• A daily life problem consist of different parts
• Input requirements (Number of inputs? Type of
  inputs? Input validation?)
• Logic requirements (How to compute the correct
  value?)
• Output requirements (Number of outputs? Type of
  outputs?)

9
Write a Program HOWTOAnalyze the logic

• A paper and a pen is always useful
• Write down the important parts
• Draw some diagrams to illustrate the logic
• Make sure you understand the logic completely
• Usually your diagrams can be transform to
  programming constructs like looping, conditional
  statements

10
Write a Program HOWTOImplement the program

• After an analysis of program requirements (input,
  output, processing logic, etc), you should have
  sufficient understanding of the program
• With the diagrams on your paper, its easy to
  transform them into C statements

11
Write a Program HOWTOTest your program

• Very Important to validate your program
• Some sample input and output are given
• Serve as the input/output requirement AS WELL AS
  some test cases
• Derive some test cases
• For common cases
• For special cases

12
Good Practices

• Comments
• Help you and your colleagues to understand and
  maintain the codes
• Indentations and spacing
• Improve the readability
• Have NO impact on compiler
• Design and THEN code
• Make sure you know what you are doing!
• Its a waste of time to design and code at the
  same time

13
Good Practices

• Initialization
• C compiler will not give you a compilation
  errors if you use a variable which have not
  initialized!
• You should write and check your codes carefully
• Variable naming
• C compiler does not require you to give
  meaningful name for variables
• But a meaningful one will help yourself and
  others to understand and maintain (and write) the
  codes
• numApple vs a

14
Good Practices

• Clarity and efficiency
• Both are important
• But try to avoid messy codes
• Fewer number of lines DOESNT imply its better
• Opening and closing braces
• Always add a pair of for if, for, while
  statements
• Always add a pair of () for complex boolean
  expressions
• Also. always add a break-statements in switch!
• Sometimes, its not necessary to add the braces
  but it could avoid certain types of errors and
  improve the readability

15
Example

• Leap year program in Lab 2
• Analysis and breakdown
• Display the prompt message and get the year from
  user
• Check if the year is leap or not (number of days
  in a year)
• Output the number of days and leap/non-leap for
  the inputted year

16
Example

• Diagram for leap year checking

Divisible by 4?
True
False
Divisible by 400?
NOT a Leap year
False
True
Divisible by 100?
Leap year
True
False
Leap year
NOT a Leap year
17
Example - Implementation
// Leap year calculation program include
ltiostreamgt using namespace std void
main() int year //year for leap year
checking int day //days in a year. //
leap year input cout ltlt "Leap Year
Calculation"ltltendl cout ltlt "Enter the year
" cin gtgt year // calculate number of days in
year if(year 4 ! 0) //NOT Leap year if not
divisible by 4 day 365 else if(year 400
0) //Leap year if divisible by 400 day
366 else if(year 100 0) //NOT leap year if
divisible by both 100 4, but not 400 day
365 else //Leap year if all
previous condition not satisfied day
366 //print out if the year is a leap year or
not if (day 366) cout ltlt year ltlt " is a Leap
year." ltlt endl else cout ltlt year ltlt " is
NOT a Leap year." ltlt endl //print out the
number of days in the year. cout ltlt "The number
of days in year " ltlt year ltlt " is " ltlt day ltlt "."
ltlt endl
18
Example

• Testing
• Identify some normal and special cases
• Year 2000
• Year 1900
• Year 1996
• Year 1998

19
End