Expressions and Assignment Statements

Expressions and Assignment Statements: AP Computer Science A Study Guide

Howdy, code cadets! Ready to dive into the thrilling world of Java expression and assignment statements? Think of this as learning the magic spells that make computers do what you want. So, grab your wand (well, keyboard) and let’s get this coding party started. 🦄💻

Java understands math just like you do. When you add, subtract, or multiply in Java, you do it just like you'd punch numbers into a calculator or argue with your math teacher about why you need to know this stuff.

Addition, Subtraction, Multiplication

Imagine you have two Pokemon with attack points that you want to add up, or maybe you’re calculating how many more jokes you need to tell to get through this guide. Here’s how you do basic operations in Java:

Want to add 1 and 2 and store it in a variable? Easy peasy:

int a = 1 + 2;

In this case, a will be 3 (almost as magical as finding out why everyone loves Java).

Need to store a result that involves decimals? Java's got your back with double:

double b = 1.0 + 3.5;

Here, b will be 4.5 (and happiness increases by the same amount).

Other basic operations work similarly:

int c = 3 - 5; // c will be -2
double d = 24 * 1.0; // d will be 24.0

The = sign is not just an equal sign; it's the assignment operator. It first evaluates the expression and then stores the result in the variable on the left. Consider it the mom-friend of your code, always making sure everything is settled properly.

And remember kids, if you mix an integer with a double, the result will be a double. Safety first!

Sometimes, you need to add or subtract 1 (like counting up all the ways you can annoy your sibling). Here are three ways to add 1 to a value:

int score = 0;
score = score + 1;
score += 1;
score++;

All three of these methods will make score equal to 1. All roads lead to Rome, or in this case, to 1.

For subtraction, it’s pretty similar:

score = score - 1;
score -= 1;
score--;

Poor score is back to zero again. But at least now it knows subtraction well.

The modulo operator (%) is like your algebra teacher's favorite trick - taking the remainder after division. It’s useful for checking if a number is even, among other things. Here’s how it works:

int a = 4 % 2; // a will be 0 (even!) 
int b = 10 % 3; // b will be 1 
int c = 3 % 5; // c will be 3

So, use modulo and you will always know how much will be left after sharing your Pizzas!

Division in Java can be a little tricky. Integer division will only give you the whole number part of the quotient, like this:

int a = 5 / 2; // a will be 2

But if you want the complete result with decimals, use a double:

double b = 5 / 2.0; // b will be 2.5

Integer division truncates the result, whereas double division gives you the exact result. Pizza slices, anyone?

Java follows the same order of operations you learned in algebra (Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction). Just remember: My Dear Aunt Sally (Multiplication/Division before Addition/Subtraction).

Here's an example for some brain exercise:

int a = 3 + 4 / 3 * (4 - 1); // a will be 6
double b = (3 * 5 / 2) / (2.0 + 8); // b will be 0.7
int c = 4 % 3 + 2 * 5 / 4;  // c will be 3
int d = (3 * 5 / 2) / (2 + 8); // d will be 0

Let's see if you can decode these magic spells (code snippets) and find the results:

1. What are the values of a, b, and c after this code executes?

int a = 1;
int b = 2;
int c = 3;
a = c;
b = b * 2;
c = 4;

The correct answer is D. a = 3, b = 4, c = 4.

2. And what about p, q, and r here?

int p = 3;
int q = 4;
int r = 5;
p = q;
q = q + 1;
r = r * 2;

The correct answer is D. p = 4, q = 5, r = 10.

By decoding these spells (or lines of code), you get to practice and master the craft of Java!

• Assignment Operator: The = sign assigns the value on the right to the variable on the left.
• Double: A type in Java for numbers with decimals. Think of it as the flexible gymnast of numeric types.
• Int: Short for integer, this type stores whole numbers without any frills.
• Modulo Operator: Represented by %, it gives the remainder of a division. Ever wonder how many cupcakes you had after the party? This operator will tell you!
• Order of Operations: Just like in algebra, PEMDAS rules all calculations.
• System.out.println: The Java statement for printing output to the console. It’s like shouting your code's results from the rooftops!

So there you go, code conquerors! You've got the lowdown on expressions and assignment statements in Java. Keep practicing, and soon you'll be coding circles around your friends. Remember, the best way to learn is to write and run lots of code. Until next time, keep calm and code on! 🚀👨‍💻👩‍💻