Conditional Expressions and Statements : 01/19/2024
Operations on Variables : 01/18/2024
Variables and Types : 01/17/2024
Welcome to CS 124 : 01/16/2024
Loops
for (inti=0; i<8; i++) {
System.out.println("Hi!");
}
This lesson presents the final core computer capability: the ability to repeat something multiple times.
By combining this with our ability to store and manipulate data and make decisions, we can truly solve any problem.
So let’s get started!
Let’s meet our first loop.
It’s the simplest one in Java, and repeats a block of code while a condition is true:
inti=0;
while (i<8) {
i++;
}
The while loop declaration looks quite similar to the if statements we’ve already seen.
First the keyword while, followed by a conditional expression inclosed in parantheses, followed by a block.
However, unlike the if statement which only executes once, the while statement continues to execute the block as long as the condition evaluates to true.
This can cause problems!
While while is the simplest loop, probably the most common loop you’ll encounter is called a for loop.
It’s more complicated than a while loop, but designed to capture a common loop programming pattern.
We frequently want to use a loop to increment a variable starting at zero and ending when it reaches some value.
(We’ll see why tomorrow.)
inti=0;
while (i<8) {
System.out.println(i);
}
This is so common that Java provides a second loop that captures this pattern.
Let’s go through it together:
There is one important difference between this while loop:
inti=0;
while (i<8) {
i++;
}
and this for loop:
for (inti=0; i<8; i++) {
}
Let’s try and figure out what it is!
inti=0;
while (i<8) {
i++;
}
Homework Restricted to Current CS 124 Students
A publicly-accessible version of this content is available at learncs.online.
Practice: Victory Loop
Created By: Geoffrey Challen
/ Version: 2020.8.0
Let's write a simple loop. Assuming an int variable named repeat has been declared and
initialized to a value larger than or equal to zero, write a loop that prints "Victory!" repeat times on separate
lines. You may use any kind of loop you want! But do not modify the value of repeat.
For this problem we're expecting only a snippet of code.
Let’s explore the connection between the two types of loop using a diagram.
Homework Restricted to Current CS 124 Students
A publicly-accessible version of this content is available at learncs.online.
Practice: Number Loop
Created By: Geoffrey Challen
/ Version: 2021.8.0
Let's write a simple loop.
Assuming an int variable named count has been declared and initialized to a value larger than zero, write a
loop that prints the numbers between 0 and count - 1, inclusive, one number each line.
So if count is 4, you should print:
0
1
2
3
You can use any kind of loop you want!
But do not modify count.
For this problem we're expecting only a snippet of code.
Don't provide a method or class declaration.
Homework Restricted to Current CS 124 Students
A publicly-accessible version of this content is available at learncs.online.
Homework: Descending Number Loop
Created By: Geoffrey Challen
/ Version: 2022.8.0
Let's write a simple loop.
Assuming an int variable named count has been declared and initialized to a value larger than zero, write a
loop that prints the numbers from count down to 0, inclusive, one number each line.
So if count is 4, you should print:
4
3
2
1
0
You can use any kind of loop you want!
But do not modify count.
For this problem we're expecting only a snippet of code.