1. Introduction to Computer Programming
CS 126
Lecture 7
Zeke Maier

2. Plan for Today Questions Administrivia Conditionals
AD Exercises 4.2 & 4.3
Assignment

3. Questions Boolean backed by 1/0? 3 == true (syntax error) Windows 7…
Recovery.gov
Microsoft job cuts

4. Administrivia http://students.cec.wustl.edu/~ejm3/
Lab assignment 1 due this afternoon!
Lab assignment 2 assigned today

5. Conditional Statements
Allows us to change the behavior of the program based on certain conditions
Example: absolute value
If (condition) {
//Statements to execute if the condition is true }
else {
//Statements to execute if the condition is false }
How would we write a method to calculate the abs value for us
Now let’s shorten it:
double abs(double x) {
if (x >= 0)
return x;
return -x; }
How about even vs. odd method

6. Conditionals
Write a method producing the same output (y values) given the same input (x values) as the function below:

7. Chained Conditionals Useful when there are more than 2 discrete cases?
if (condition) {
//Statements to execute if the condition is true
} else if() {
//Statements
} else { }

8. Example if (x > 0) { System.out.println(“1”); } else if( x == 7) {
} else if(false) {
System.out.println(“3”);
} else if(x<=0 && x > -100) {
System.out.println(“4”);
} else {
System.out.println(“5”); }
Input is any whole number…
Which outputs can we get from this chained conditional?
What about if we changed the first if to true
What if we removed the else?

9. Nested Conditionals
If (condition) {
if (condition2){
//Statements
} else { }
} else {
You can also nest a conditional inside another
tabbing can help read through the code
In general it is a bad idea to have too much nesting…
If (year%4 == 0)
if (year %100 == 0)
if (year %400 ==0)
leap year
else
not
Leap year!
Else
How would you write a conditional to determine if a year was a leap year?

10. Shortening Conditionals
If the body of the conditional is a single line, then braces (‘{‘) are not needed.
Avoid using a conditional just to return the value of a test
Do not write unnecessary else conditions
if (condition) return condition;
return true;
else
return false;

11. AD Exercises 4.2 & 4.3
If you are given three sticks, you may or may not be able to arrange
Exercise 4.2
them in a triangle. For example, if one of the sticks is 12 inches long and the other
two are one inch long, it is clear that you will not be able to get the short sticks to
meet in the middle. For any three lengths, there is a simple test to see if it is possible
to form a triangle:
“If any of the three lengths is greater than the sum of the other two,
then you cannot form a triangle. Otherwise, you can.”
Write a method named isTriangle that it takes three integers as arguments, and that
returns either true or false, depending on whether you can or cannot form a triangle
from sticks with the given lengths.
The point of this exercise is to use conditional statements to write a method that
returns a value.
a. Write the number 1 next to the first statement of this program that will be
executed. Be careful to distinguish things that are statements from things that
are not.
b. Write the number 2 next to the second statement, and so on until the end of
the program. If a statement is executed more than once, it might end up with
more than one number next to it.
c. What is the value of the parameter blimp when baffle gets invoked?
d. What is the output of this program?

12. Assignments Lab 1 due today! Lab 2 assigned today Readings Friday
AD Appendix A & B
KG Notes