2. How to develop a program?
Requirements
Problem Analysis
Design
Designing algorithm
Pseudo code
Flow chart
Implementation
Implementing algorithm in c/c++
Validation
Test
Maintenance
Refinement
Software
Development
Life-Cycle

3. Requirements Discovery
Write a program to compute an employee's weekly pay?
Problem Analysis
Problem Identification
Abstraction
Inputs and outputs determination
Defining their relation
How many hours did you work?
How much do you get paid per hour?
employee's weekly pay equal to multiplication of Hours by Pay Rate

4. Problem vs. Solution A problem is something that causes trouble
The solution is how to solve or fixe the problem

5. Algorithm
A procedure for solving a problem in terms of actions and the order in which these actions are to be executed in a computer program (program control)
Action
Order

6. Execution order
Sequential execution, normally, statements in a program are executed one after the other in the order in which they’re written
Various C statements enable you to specify that the next statement to be executed may be other than the next one in sequence. This is called transfer of control

7. Structured Programming
goto statement that allows programmers to specify a transfer of control to one of many possible destinations in a program
Research had demonstrated that programs could be written without any goto statements
Programs produced with structured techniques were clearer, easier to debug and modify and more likely to be bug free in the first place.
Research had demonstrated that all programs could be written in terms of only three control structures, namely the sequence structure, the selection structure and the repetition structure

8. Pseudo code
An artificial and informal language that helps you develop algorithms
similar to everyday English
are not executed on computers
consists only of action statements
pay-calculation program:
Read Hours and Pay Rate
weekly pay = Read Hours * Pay Rate

9. Flowchart
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
A flowchart is a diagram that depicts the flow of an algorithm
pay-calculation program
Each symbol represents a different type of operation

10. Terminals represented by rounded rectangles
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
Terminal
represented by rounded rectangles
indicate a starting or ending point
START
END
Flow line
Terminal

11. Input/Output Operations
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
indicate an input or output operation
Display message “How many hours did you work?”
Input/Output Operation
Read Hours

12. Processes
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
indicates a process such as a mathematical computation or variable assignment
Multiply Hours by Pay Rate. Store result in Gross Pay.
Process

13. Execution Variable Contents: Hours: ? Pay Rate: ? Gross Pay: ?
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
Output Operation
How many hours did you work?
Variable Contents: Hours: ? Pay Rate: ? Gross Pay: ?

14. Execution Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
Input Operation
(User types 40)
How many hours did you work? 40
Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?

15. Execution Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
How much do you get paid per hour?
Output Operation
Variable Contents: Hours: 40 Pay Rate: ? Gross Pay: ?

16. Execution Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: ?
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
How many hours did you work? 20
Input Operation
(User types 20)
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: ?

17. Execution Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
How many hours did you work? 20
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
Process
(Gross Pay = Hours * Pay Rate)

18. Execution Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
START
Display message “How many hours did you work?”
Read Hours
Display message “How much do you get paid per hour?”
Read Pay Rate
Multiply Hours by Pay Rate. Store result in Gross Pay.
Display Gross Pay
END
Your gross pay is 800
Variable Contents: Hours: 40 Pay Rate: 20 Gross Pay: 800
Output Operation

19. Connectors Sometimes a flowchart will not fit on one page
A connector (represented by a small circle) allows you to connect two flowchart segments A
START
END

20. Call calc_pay function
Modules
A program module (such as a function in C) is represented by a special symbol
The position of the module symbol indicates the point the module is executed
A separate flowchart can be constructed for the module
START
END
Read Input
Call calc_pay function
Display results
module

21. Control Structures Sequence Decision selection statement
The if statement is called a single-selection statement because it selects or ignores a single action.
The if…else statement is called a double-selection statement because it selects between two different actions.
The switch statement is called a multiple-selection statement because it selects among many different actions
Repetition
while
do…while
for

22. Sequence Structure a series of actions are performed in sequence
The pay-calculating example

23. Compound Statements
A statement is a specification of an action to be taken by the computer as the program executes
Compound Statements is a list of statements enclosed in braces, { }

24. Decision Structure
One of two possible actions is taken, depending on a condition
Selection structures are used to choose among alternative courses of action
YES NO
YES NO
x < y?
Process B
Process A

25. C programming language
Decision Structure
The flowchart segment below shows how a decision structure is expressed in C as an if/else statement
Flowchart
C programming language
YES NO
x < y?
Calculate a as x times 2.
Calculate a as x plus y.
if (x < y)
a = x * 2;
else
a = x + y;

26. Example
Compound statement is way to group many statements together so they are treated as one
if (grade >= 60)
printf( "Passed.\n" ); // { printf( "Passed.\n" ); }
else {
printf( "Failed.\n" );
printf( "You must take this course again.\n" ); }

27. C programming language
Decision Structure
The flowchart segment below shows a decision structure with only one action to perform
Flowchart
C programming language
YES NO
x < y?
Calculate a as x times 2.
if (x < y)
a = x * 2;

28. Combining Structures YES NO if (x > min) { if (x < max)
Display “x is within limits.”
Display “x is outside the limits.”
YES NO
x > min?
x < max?
if (x > min) {
if (x < max)
printf("x is within the limits");
else
printf("x is outside the limits"); }

29. Example int k = 1, m = 4; if (k < 2 || m == 3) { m = 2 + k;
printf("%d", m); }
else
k = 1;
printf("%d", k);
int k = 1, m = 4;
if (k < 2 || m == 3) {
m = 2 + k, printf("%d", m); }
else
k = 1, printf("%d", k);
Which is more readable?

30. Example if(x) if(x) if(x) if(y) { { printf("Yes"); if(y) if(y) else
printf("No");
if(x) {
if(y)
printf("Yes");
else
printf("No"); }
if(x) {
if(y)
printf("Yes"); }
else
printf("No");
if (x < 0.25)
count1++;
else if (x >= 0.25 && x < 0.5)
count2++;
else if (x >= 0.5 && x < 0.75)
count3++;
else
count4++;
if (x < 0)
sign = -1;
else if (x == 0)
sign = 0;
else
sign = 1;

31. Case Structure
One of several possible actions is taken, depending on the contents of a variable

32. Case Structure
indicates actions to perform depending on the value in years_employed
If years_employed = 2, bonus is set to 200
If years_employed = 3, bonus is set to 400
CASE years_employed 1 2 3
Other
bonus = 100
bonus = 200
bonus = 400
bonus = 800
If years_employed = 1, bonus is set to 100
If years_employed is any other value, bonus is set to 800

33. switch
A switch statement allows a single variable (integer or char) to be compared with several possible constants
A constant can not appear more than once, and there can only be one default expression

34. switch switch (variable) { case const: statements...; default: }
switch (c = toupper(getch())) {
case ‘R’:
printf("Red");
break;
case ‘G’:
printf("Green");
default:
printf("other"); }
switch (variable) { case const: statements...; default: }

35. Example switch(betty) { case 1: printf("betty = 1\n"); case 2: case 3:
CASE betty? 1 2 3
Other
betty = 1
switch(betty) {
case 1:
printf("betty = 1\n");
case 2:
printf("betty=2\n");
break;
case 3:
printf("betty=3\n");
default:
printf("Not sure\n"); }
betty = 2
betty = 3
Not sure

36. Repetition Structure
A loop tests a condition, and if the condition exists, it performs an action. Then it tests the condition again. If the condition still exists, the action is repeated. This continues until the condition no longer exists
x < y?
Process A
YES

37. C programming language
Repetition Structure
The flowchart segment below shows a repetition structure expressed in C as a while loop
Flowchart
C programming language
x < y?
Add 1 to x
YES
while (x < y)
x++;

38. While while (loop_repetition_condition) statement; OR
//Compound statement {
statement1;
statement2; // … }

39. Controlling a Repetition Structure
The action performed by a repetition structure must eventually cause the loop to terminate. Otherwise, an infinite loop is created
In this flowchart segment, x is never changed. Once the loop starts, it will never end
How can this flowchart be modified so it is no longer an infinite loop?
x < y?
Display x
YES

40. Controlling a Repetition Structure
Adding an action within the repetition that changes the value of x
x < y?
Display x
Add 1 to x
YES

41. A Pre-Test Repetition Structure
This type of structure is known as a pre-test repetition structure. The condition is tested BEFORE any actions are performed
if the condition does not exist, the loop will never begin
x < y?
Display x
Add 1 to x
YES

42. Example int counter = 0; while (counter < 1000) ; while (1);
printf("%d\n", counter ++);
int counter = 9;
while (counter > 0)
printf("%d\n", counter --);
int counter = 0;
while (counter < 9) {
printf("%d\n", counter);
counter++; }
int counter = 0;
while (counter < 9) {
printf("%d\n", counter ++); }

43. A Post-Test Repetition Structure
The condition is tested AFTER the actions are performed
A post-test repetition structure always performs its actions at least once
Display x
Add 1 to x
YES
x < y?
C programming language
do { printf(…); x++; } while (x < y);

44. do-while
do statement; while (loop_repetition_condition) OR do //Compound statement { statement1; statement2; // … }

45. Example Draw a flowchart for the following problem:
Read 5 integer and display the
value of their summation.
Input : 5 integer
n1, n2, n3, n4, n5
Output: The summation of
n1, n2, .., n5
Input example:
Output example: 20

46. Assume input example:
start
Input n1 2 n1
Input n2 3 n2
This flowchart does not use loop, hence we need to use 6 different variables
Input n3 4 n3
input n4 5 n4
input n5
sum ← n1+n2+n3+n4+n5 6 n5
output sum 20
sum
end

47. This loop is Uses only The counter counter-controlled 3 variables
Assume input
example: 3 2 1 4 6 5
counter
counter ← 1, sum ← 0 2 20 9 14 5
sum
14 + 6
5 + 4
9 + 5
2 + 3
0 + 2
counter < 6
false
6 < 6 false
5 < 6 true
3 < 6 true
2 < 6 true
1 < 6 true
4 < 6 true
true 4 6 3 2 5
input n n
sum ← sum + n
counter++
This loop is
counter-controlled
The counter
Increases by 1
Uses only
3 variables
output sum

48. Decreasing Counter-Controlled Loop
counter ← 5, sum ← 0
counter > 0
false
true
input x
sum←sum+ x
counter--
output sum
C Programming Language

49. For for (initial_value ; condition; update_counter)
statement; OR
// Compound statement
for (initial_value ; condition; update_counter) {
statement; // … }

50. int x, sum, i; sum = 0; for (i = 0; i < 5; i++) { scanf(“%d”,&x);
counter ← 1, sum ← 0
int x, sum, i;
sum = 0;
for (i = 0; i < 5; i++) {
scanf(“%d”,&x);
sum = sum + x; }
counter < 6
false
true
input n
sum ← sum + n
counter++
printf(“%d”,sum);
output sum 50

51. ???
num
Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); printf(“have come to exit\n”); _ 51

52. 1
num
Example: for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); printf(“have come to exit\n”); _ 52

53. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num _ 53

54. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 _ 54

55. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 2
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 _ 55

56. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 2
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 _ 56

57. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 2
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 _ 57

58. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 _ 58

59. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 _ 59

60. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 3 _ 60

61. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 4
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 3 _ 61

62. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 4
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 3 _ 62

63. for (num = 1; num <= 3; num++ ) printf(“%d\t”, num); 4
Example:
for (num = 1; num <= 3; num++ )
printf(“%d\t”, num);
printf(“have come to exit\n”);
num
1 2 3 have come to exit_ 63

64. Example * ** *** **** ***** ****** #include <stdio.h> int main(){
int iCounter = 0;
int jCounter = 0;
while (iCounter < 7)
jCounter = 0;
while (jCounter < iCounter)
printf("*");
jCounter++; }
printf("\n");
iCounter++;
getch();
return 0;