📘 College Board Notes — Sequencing

✅ What is Sequencing?

Sequencing means running instructions in a specific order, one step at a time.

Computers execute instructions exactly in the order they are written unless told otherwise.

🎯 Why Sequencing Matters (College Board Perspective)

Programs are built using:

• Sequencing
• Selection (decisions)
• Iteration (loops)

Sequencing is the foundation of all programs.

🧠 Key Idea

• ✅ Computers do exactly what you tell them.
• ❌ Computers do NOT guess what you meant.

The order of instructions directly affects program output.

📌 Real-World Examples

Logging Into a System

1. Open browser
2. Enter username
3. Enter password
4. Click login

ATM Withdrawal

1. Insert card
2. Enter PIN
3. Select withdrawal
4. Receive cash

💻 Programming Example (Java)

Correct Sequencing

int a = 5;
int b = 10;
int sum = a + b;

System.out.println(sum);

Incorrect Sequencing

int sum = a + b;   // ERROR
int a = 5;
int b = 10;

🔥 Execution Flow

Programs execute:

• Top to bottom
• One line at a time

System.out.println("Step 1");
System.out.println("Step 2");
System.out.println("Step 3");

⚠️ Common Student Mistakes

• Using variables before declaring them
• Using input before reading it
• Incorrect order of operations

🔍 Tracing Example (AP Style)

int x = 3;
x = x + 2;
x = x * 4;

System.out.println(x);

Output: 20

🧪 Mini Practice

int a = 2;
int b = 3;

System.out.println(a + b);
a = 10;
System.out.println(a + b);

Output:

5
13

⭐ Big Ideas to Remember

• Programs run top → bottom
• Changing order changes results
• Variables must exist before use
• Sequencing is the foundation of programming

🎓 College Board Vocabulary

• Algorithm — step-by-step procedure
• Execution — running program instructions
• Statement — single instruction
• Program Flow — order instructions run