1. CS2011 Introduction to Programming I Selections (I)
Chengyu Sun
California State University, Los Angeles

2. Mortgage Calculator Revisited
The formula
How do we include the case where monthly interests rate is 0?
Check if the interest rate entered is 0,
and based on the result, select different
part of the program to execute.

3. What's Needed in a Programming Language
Branch Statement
Check if the interest rate entered is 0,
and based on the result, select different
part of the program to execute.
Boolean Expression
Boolean Value

4. Boolean Expressions
Used to check a condition, and the result would be either true or false (i.e. boolean)
For example:
interestRate == 0
radius > 0

5. Relational Operators Notice the difference between = and ==
Name
<
Less than
<=
Less than or equal to
>
Greater than
>=
Greater than or equal to ==
Equal to !=
No equal to
Notice the difference between = and ==
In Java, relational operators can only be used on numbers

6. Boolean Values and Variables
boolean is a data type just like int and double
There are only two possible boolean values: true and false
Boolean variables can be use to store boolean values (usually the results of some condition checks)
Example: SimpleBooleans.java

7. Example: Addition Quiz
Generate two random numbers between 0 and 10
Ask the user to enter the sum of the two numbers
Display true or false depending on whether the answer is correct
Use java.util.Random to generate the random numbers

8. Branch Statements if statement condition if-else statement condition
true
condition
if-else statement
true
condition
false

9. if statement
if ( boolean-expression ) {
statement(s); }
If the boolean expression evaluates to true, execute the statement(s) in {}
{} can be omitted if there's only one statement

10. If-else statement if ( boolean-expression ) { statement(s); } else {
If the boolean expression evaluates to true, execute the statement(s) in {} after if (a.k.a. the if block), otherwise execute the statements in {} after else (a.k.a. the else block)
{} can be omitted if there's only one statement in the block

11. Examples
Modify Addition Quiz so it display correct/incorrect instead of true/false
Use if statement
Use if-else statement
Modify Mortgage Calculator to handle the case where the interest rate is 0

12. Check Multiple Conditions
Example: LetterGrade.java
Conditions
Letter Grade
score >= 90 A
80 <= score < 90 B
70 <= score < 80 C
60 <= score < 70 D
score < 60 F

13. Use Nested if-else Statements
Write proper conditions
Understand that certain conditions are already met when we get to the else block
Use proper syntax
else{
if(){ }
else if(){ }
else{