#AP Computer Science A: Expressions and Assignment Statements - The Night Before 🚀

Hey! Let's make sure you're totally ready for tomorrow. This guide will help you nail those tricky questions on expressions and assignment statements. Let's dive in!

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1. Numeric Types and Basic Math in Java

# Basic Math Operations

Java handles addition, subtraction, and multiplication just like your calculator. Remember to use variables to store results.

java
int a = 1 + 2; // a is 3
double b = 1.0 + 3.5; // b is 4.5
int c = 3 - 5; // c is -2
double d = 24 * 1.0; // d is 24.0

• Assignment Operator (=): Evaluates the expression on the right and stores the result in the variable on the left.
• Integer vs. Double:
  • int operations with int result in an int.
  • Operations with at least one double result in a double.

# Incrementing and Decrementing

There are multiple ways to add or subtract 1 from a variable:

• Adding 1:
  • score = score + 1;
  • score += 1;
  • score++;
• Subtracting 1:
  • score = score - 1;
  • score -= 1;
  • score--;

# Modulo Operator (%)

The modulo operator % gives you the remainder of a division. Only works with integers where the divisor (b) is positive.

java
int a = 4 % 2; // a is 0 (4 = 2 * 2 + 0)
int b = 10 % 3; // b is 1 (10 = 3 * 3 + 1)
int c = 3 % 5; // c is 3 (3 = 0 * 5 + 3)

# Division

Division can be tricky! Pay close attention to data types.

java
int a = 5 / 2; // a is 2 (integer division)
double b = 5 / 2.0; // b is 2.5 (double division)

• Integer Division: Returns only the whole number quotient (truncates the decimal).
• Double Division: Returns the actual quotient as a decimal.

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2. Order of Operations

Java follows the standard order of operations (PEMDAS/BODMAS), with modulo included with multiplication and division.

#Practice with Order of Operations

Let's break down some examples:

java
int a = 3 + 4 / 3 * (4-1);
double b = (3 * 5 / 2) / (2.0 + 8);
int c = 4 % 3 + 2 * 5 / 4;
int d = (3 * 5 / 2) / (2 + 8);

a = 3 + 4 / 3 * (4 - 1) = 3 + 4 / 3 * 3 = 3 + 1 * 3 = 3 + 3 = 6
b = (3 * 5 / 2) / (2.0 + 8) = (15 / 2) / (10.0) = (7) / (10.0) = 0.7
c = 4 % 3 + 2 * 5 / 4 = 1 + 2 * 5 / 4 = 1 + 10 / 4 = 1 + 2 = 3
d = (3 * 5 / 2) / (2 + 8) = (15 / 2) / (10) = (7) / (10) = 0

#3. Practice Problems

Let's solidify your understanding with some practice problems. These are designed to mimic the types of questions you'll see on the exam.

# Basic Math Practice

What are the values of a, b, and c after the following code executes?

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

Answer

D. a = 3, b = 4, c = 4

What are the values of p, q, and r after the following code executes?

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

Answer

D. p = 4, q = 5, r = 10

What are the values of x, y, and z after the following code executes?

java
int x = 2;
int y = 3;
int z = 4;
x = z;
y = y + 2;
z = x * y;

Answer

B. x = 4, y = 5, z = 20

What are the values of m, n, and o after the following code executes?

java
int m = 5;
int n = 6;
int o = 7;
m = n;
n = o;
o = m + n;

Answer

A. m = 6, n = 7, o = 13

What are the values of x, y, and z after the following code executes?

java
int x = 3;
int y = 4;
int z = 5;
x = x * 2;
y = y + 3;
z = z - 1;

Answer

D. x = 6, y = 7, z = 4

What are the values of x, y, and z after the following code executes?

java
int x = 0;
int y = 1;
int z = 2;
x = y - z;
y = x + y;
z = x - y;

Answer

A. x = -1, y = 0, z = -1

What are the values of x, y, and z after the following code executes?

java
int x = 3;
int y = 4;
int z = 5;
x = y / x;
y = z / y;
z = x / z;

Answer

B. x = 1, y = 1, z = 0

# Modulo Practice

What is the result of 50 % 10?

Answer

C. 0

What is the result of 15 % 4?

Answer

B. 3

What is the result of 100 % 7?

Answer

C. 2

What is the result of 9 % 3?

Answer

A. 0

What is the result of 25 % 5?

Answer

A. 0

What is the result of 12 % 10?

Answer

B. 2

What is the result of 7 % 10?

Answer

A. 7

What is the result of 3 % 10?

Answer

C. 3

What is the result of 0 % 10?

Answer

B. 0

What is the result of 2 % 10?

Answer

A. 2

# AP CSA-Style Practice

What is printed when the following code segment is executed?

java
int a = 8;
int b = 3;
double c = 2.0;
System.out.println(7 + a / b * c - 1);

Answer

C. 10.0

What is printed when the following code segment is executed?

java
int a = 12;
int b = 4;
double c = 5.0;
System.out.println(3 + a / b * c - 2);

Answer

A. 16.0

What is printed when the following code segment is executed?

java
int a = 10;
int b = 5;
double c = 3.0;
System.out.println(2 + a / b * c - 3);

Answer

E. 5.0

What is printed when the following code segment is executed?

java
int a = 15;
int b = 6;
double c = 4.0;
System.out.println(1 + a / b * c - 4);

Answer

A. 5.0

What is printed when the following code segment is executed?

java
int a = 20;
int b = 8;
double c = 6.0;
System.out.println(6 + a / b * c - 5);

Answer

D. 13.0

#Final Exam Focus 🎯

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Key Topics

• Data Types: Know the difference between int and double and how they affect operations.
• Assignment Operator: Understand how values are assigned and updated.
• Order of Operations: Be precise with PEMDAS and integer division.
• Modulo Operator: Master its use for remainders.
• Integer Division: Remember that int / int truncates the decimal.

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• Read Carefully: Pay close attention to data types and the order of operations.
• Step-by-Step: Break down complex expressions into smaller steps.
• Integer Division: Watch out for integer division; it's a common pitfall.
• Practice: The more you practice, the more comfortable you'll be.
• Show Your Work: For FRQs, show your steps to get partial credit.

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• Forgetting the order of operations.
• Incorrectly applying integer division.
• Misunderstanding the modulo operator.
• Not tracking variable changes carefully.

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Practice Question

Practice Questions

Multiple Choice Questions

1. What is the value of result after the following code executes?

java int x = 10; double y = 3.0; double result = x / 4 + y * 2; ```

A) 8.0
B) 8.5
C) 9.0
D) 9.5

2. What is the output of the following code?

```

java int a = 7; int b = 3; System.out.println(a % b + a / b); ```

A) 2
B) 3
C) 4
D) 5

Free Response Question

Consider the following class MathFun:

java
public class MathFun {
    private int value;

    public MathFun(int num) {
        value = num;
    }

    public void modify() {
        value = (value * 2) - (value % 5);
    }

    public int getValue() {
        return value;
    }

    public static void main(String[] args) {
        MathFun obj1 = new MathFun(12);
        MathFun obj2 = new MathFun(7);
        obj1.modify();
        obj2.modify();
        System.out.println(obj1.getValue() + " " + obj2.getValue());
    }
}

(a) What is the output of the main method?

(b) Explain in detail how the modify method changes the value instance variable.

Scoring Rubric

(a) Output (2 points)

• 1 point for correct output of obj1: 24 - 2 = 22
• 1 point for correct output of obj2: 14 - 2 = 12
• Correct Output: 22 12

(b) Explanation (3 points)

• 1 point for stating that the value is multiplied by 2
• 1 point for stating that the remainder of value divided by 5 is calculated.
• 1 point for stating that the remainder is subtracted from the doubled value.