COMP 202 Lecture Notes - Lecture 4: Infinite Loop, While Loop, 5,6,7,8
8 Jun 2018
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COMP 202: Foundations of Programming
Lecture 4: Loops and Arrays
If-If vs. If-Else:
The difference between these two statements is that in order for the one on the left-hand side to work, (not
condition) must become true in the midst of the statement in order for the command to be processed
→ int x = 1;
if (x > 0){
System.out.println(“Positive. Altering the value.”);
x--;
}
if (x <= 0){
System.out.println(“Not positive.”);
}
This code would print:
Positive. Altering the value.
Not positive.
→ int x = 1;
if (x > 0){
System.out.println(“Positive. Altering the value.”);
x--;
}
else (x <= 0){
System.out.println(“Not positive.”);
}
This code would print:
Positive. Altering the value.
If-else If-else statements:
For when you have a more complicated set of conditions with 2+ options
Option 1: Nested if-else statements:
if (condition 1){
//commands
} else{
if(condition 2){
//commands
} else{
if (condition 3){
//commands
}
}
COMP 202: Foundations of Programming
}
Option 2: All at the same level:
if (condition 1){
//commands
} else if (condition 2){
//commands
} else if (condition 3){
//commands
} else {
//commands
}
Order Matters:
Much like else, the “else if” is only executed if the prior conditions were false. So, there can be a
big difference if the order of the options is changed
Omitting Curly Brackets:
People do it. Don’t do it.
The Math Library:
Java comes with a math library. There are many, many methods that can be used from this library. Also
contains two useful point values, e and pi, which can be accessed by Math.E and Math.PI
Some useful methods:
Math.abs(x) – absolute value of: |x|
Math.sqrt(x) – square root of: √x
Math.pow(x,y) – x to the power of y: xy
Math.sin(x) – trig sine of x, where x is in radians
Math.ceil(x) – smallest integer that is greater than or equal to the argument
If statements let us choose whether to execute some code, or to choose between multiple blocks of code to
execute. Another way to control the flow is to execute something multiple times
As a method to execute something, copy-pasting is less than ideal:
- annoying
- error prone
- difficult to maintain (hard to edit to fix mistakes)
- does not generalize
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COMP 202 Full Course Notes
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Document Summary
The difference between these two statements is that in order for the one on the left-hand side to work, (not condition) must become true in the midst of the statement in order for the command to be processed. Int x = 1; if (x > 0){ if (x <= 0){ Int x = 1; if (x > 0){ else (x <= 0){ For when you have a more complicated set of conditions with 2+ options. Option 1: nested if-else statements: if (condition 1){ Option 2: all at the same level: if (condition 1){ Much like else, the else if is only executed if the prior conditions were false. So, there can be a big difference if the order of the options is changed. There are many, many methods that can be used from this library. Also contains two useful point values, e and pi, which can be accessed by math. e and math. pi.
