1. CHAPTER 5: SELECTION STRUCTURES: if and switch STATEMENTS
Learning outcomes
Define the concept of selection structure.
Apply the if, if/else, if/else if, switch/case selection structure to select actions.
Design selection using algorithm for solving problems.
Convert problem design into C code using selection controls.
Trace an algorithm or program to verify that it does what user expect.
Write a program using selection statements that control the flow of program execution
Hanly, Koffman, C Program Design for Engineers, Second Edition, Addison Wesley, 2004.
Reference...
Prepared By: Pn. Nik Maria Nik Mahamood (Coordinator DDC 1012)
Prepared by: Pn. Nik Maria Nik Mahamood

2. This chapter introduces to:
Control Structure
Conditions
The if Statements
If Statements with Compound Statements.
Nested if Statements and Multiple-Alternative Decisions
Decision Steps in Algorithms
The switch Statement

3. CONTROL STRUCTURES
Control structure – a combination of individual instructions into a single logical unit with one entry point and one exit point.
Instruction are organized into three kinds of control structures to control execution flow: sequence, selection and repetition.
Compound statement – a group of statements bracketed by { and } that are executed sequentially.

4. { statement1; } Example: statement2; … statementN;
A selection control structire chooses which alternative to execute.

5. CONDITIONS
This topic already covered in chapter 4.
You can refer this topic at page 147 – 157 (Main TextBook).

6. if (rest_heart_rate > 56)
THE if STATEMENT
In C, the if statement is the primary selection control structure.
If statement with two alternatives
The if statement
if (rest_heart_rate > 56)
printf(“Keep up your exercise!\n”);
else
printf(“Your heart is in execllent health!\n”);
Syntax as follows:
if (ungkapan)
kenyataan;

7. Figure 4.4 Flowcharts of if Statements with (a) Two Alternatives and (b) One Alternative Source: This figure is taken from Pearson Addison-Wesley, 2004.

8. if Statement with one alternative
if (x != 0.0)
product = product * x;
Syntax as follows:
If (ungkapan)
kenyataan;
Another example
if (k < j)
min = k;
prinf(“Akhir kenyataan if\n”);
will be
executed if k < j
Always be
executed even k >= j

9. IF STATEMENTS WITH COMPOUND STATEMENTS
Example #1
if (k < j) {
min = k;
prinf(“Akhir kenyataan if\n”); }
Example #2
Both will be
executed if k < j
Source: This figure is taken from Pearson Addison-Wesley, 2004.

10. DECISISON STEPS IN ALGORITHMS
Decision step – an algorithm step that selects one of several actions.
Case study : water Bill Problem
See page

11. Figure 4.6 Structure Chart for Water Bill Problem
Source: This figure is taken from Pearson Addison-Wesley, 2004.

12. Figure 4.7 Program for Water Bill Problem
Source: This figure is taken from Pearson Addison-Wesley, 2004.

13. Figure 4.7 Program for Water Bill Problem (cont’d)
Source: This figure is taken from Pearson Addison-Wesley, 2004.

14. Figure 4.7 Program for Water Bill Problem (cont’d)
Source: This figure is taken from Pearson Addison-Wesley, 2004.

15. Figure 4.7 Program for Water Bill Problem (cont’d)
Source: This figure is taken from Pearson Addison-Wesley, 2004.
Figure 4.8 Sample Run of Water Bill Program
Source: This figure is taken from Pearson Addison-Wesley, 2004.

16. NESTED if STATEMENTS AND MULTIPLE-ALTERNATIVE DECISIONS
Nested if statements – an if statement with another if statement as its true task or its false task.
Example:
if (x > 0)
num_pos = num_pos + 1;
else {
if (x < 0)
num_neg = num_neg + 1;
else
num_zero = num_zero + 1; }

17. Comparison of nested if and sequence of if.
See Table 4.10 at page 180
Multiple – Alternative Decision form of nested if:
if (x > 0)
num_pos = num_pos + 1;
else if (x < 0)
num_neg = num_neg + 1;
else if
num_zero = num_zero + 1;

18. For more exercises, see example 4.16 at page 182 – 183
Example 4.19 at page 186 – 188 (Flowchart of example 4.19 shown as below)
Source: This figure is taken from Pearson Addison-Wesley, 2004.

19. THE switch STATEMENT
The switch statement may also be used in C to select one of several alternatives.
Used expression in implementation. This expression also known as controlling expression
The value of this expression may be of type
char
int
But not of type double

20. Figure Example of a switch Statement with Type char Case Labels Source: This figure is taken from Pearson Addison-Wesley, 2004.