LU03_Control_Structure_Selection

22
if Statement
The similarity between single selection structure and if statement: if Statement:
Single Selection: if <condition is true> start step 1 step 2 … step k end_if
16
Multiple Selection
Step a
Condition1
false
true
Step m
Condition2
false
true
Step n
Step z
17
Multiple Selection
Pseudocode Structure (Cascaded if)
step a if <condition_1 is true> start step m end_if if <condition_2 is true> start step n end_if else step x end_else step z
Exercise
13
ቤተ መጻሕፍቲ ባይዱ
Exercise - Answer
start
Verify this flowchart !
age
true “You are eligible to vote”
age > 20 false “You are not eligible to vote”
“You are <age> years old” end
24
> 15?
num1 num2
? 20
15 ? 15 20 ?
min
if - else Statement
Syntax:
if (expression) statement; else statement; if (expression) { statement1; statement2; } else statement3;
Given a mark, determine its grade based on the table below:
74 < mark < 100 64 < mark < 75 54 < mark < 65 39 < mark < 55 0 < mark < 40 others grade = A grade = B grade = C grade = D grade = E error message
Pseudocode Structure
step a if <condition is true> start step m step n end_if else start step x step y end_else step z
… additional steps at the bottom …
6
Single Selection： start flow chart
Step a
true
condition
false
Step m
Step n
Step x end
7
A Small Exercise
Develop an algorithm for the following problem:
A system to check/verify the eligibility of a person to vote during the election is going to be developed. The input for the system is the person’s age. If the age is greater than 20 years old, then display “You are eligible to vote” After that, no matter what age the person is, the system will display “You are <age> years old” message.
1. 2. 3. 4. 5. 6. 7. 8. 9. if…else… switch...case… for while do …while continue break goto return Selection/Branch
Loop
Control transfer
3
Control Structure: Selection/Branch
Knowledge: Understand the various concepts of selection control structure
Skill: Be able to develop a program involving selection control structure
4
Selection Structure
27
Example: if – else
void main() { int mark;
Statement
What will the output be if the mark is 74?
printf(“Mark:”); scanf(“%d”, &mark); What will the output if (mark >= 50) be if the mark is 14? printf(“Pass\n”); else printf(“Fail\n”); printf(“Your mark is %d”, mark); }
28
if – else - if Statement
Syntax: if (expression) statement; else if (expression) statement; else if (expression) statement; else statement;
25
or
if – else Statement
The similarity between double selection structure and if else statement: if-else Statement:
Double Selection: if <condition is true> start step 1 … step k end_if else start step 1 … step n end_else if (<condition> ) { statement 1 … statement k } else { statement 1 … statement n }
8
Exercise - Answer
start start Assume the age is 12 years old age
true
12 > 20 ? FALSE ! age > 20 false “Your are age <age> is <age> Your age is 12 years“You years old” years old” old
20
if Statements
if if - else
if – else - if
21
if Statement
The structure is similar to single selection (flowchart) Syntax: if (expression) statement; or if (expression) { statement1; statement2; }
selection look like ?
15
Multiple Selection
Pseudocode Structure (Multi-way if)
step a if <condition_1 is true> start step m end_if if <condition_2 is true> start step n end_if step z
“You are eligible to vote”
end
9
Single Selection
Pseudocode Structure Single Selection
step a if <condition is true> start step m step n end_if step x
10
Double Selection
26
if - else Statement
Example:
if (num1 < num2) 10 < 15? min = num1; else min = num2; printf(“Smallest: %d\n”, min);
Smallest: 10 _ _
num1 num2
10
15 10 ?
min
18
Multiple Selection
Step a Condition1
false true
Step m Step n
Condition2
false
true
Step x
Step z
19
Warming up
Develop a flowchart for the following problem.
Single Selection Double Selection
Multiple Selection
5
Single Selection： Pseudo-code description