3.1 Variables and Assignments

1. Exam Points

• Use the assignment operator to assign a value to a variable.
• Predict output of a variable after some assignment steps.
• Select the correct data type for a given piece of data.
• Benefits of well-named variables. (more readable and easy to modify)
• How to swap the values of two variables. (use a third variable temp)

2. Knowledge Points

(1) Programming Languages

• Programming languages are categorized by their level of abstraction from the computer's hardware to:
  • Low-level : assembly language(汇编语言), machine language(机器语言).
    • high execution efficiency, high control over hardware.
    • complex, lack of portability(可移植性)
    • Assembly language is a specific type of low-level language. It uses (mnemonic symbol) for instructions.
  • High-level : Python, Java, C++, C#, JavaScript, etc.
    • resembles natural language and increase readability
    • portability
    • slower execution and less control over hardware
• Assembly language is a specific type of low-level language. It uses (mnemonic symbol-助记符) for instructions.

(2) Variables (变量)

• A variable is an abstraction inside a program that can hold a changable value.
• Using meaningful variable names helps with the readability of program code and understanding of what values are represented by the variables. (readable and easy to modify)
• Some programming languages connect data types to variables.
• Commonly used types include:
  • integer: whole number, no decimal point.
    • Ex. 10, 200
  • fractional number: with a decimal point, also called floating numbers/real numbers.
    • Ex. 2.56
  • Boolean: either true or false.
  • String: an ordered sequence of characters.
    • Ex. Annabelle, 13697665261
  • list: a collection of data.
    • Ex. [10, 20, 40, 50, 60]
  • number: integers and fractional numbers.
    • 100, 2.5

(3) Assignment Operator (赋值运算符)

• The assignment operator is used to initialize or change the value represented by a variable.

• The value stored in a variable will be the most recent value assigned.

• Assignment operator in AP CSP (pseudocode):
  

  

• Input and Output in AP CSP:
  

  

• Examples:
  

  • a ← INPUT()
  • DISPLAY(a)
  • DISPLAY("Annabelle")

• Swap(交换) the values of two variables. You need to use a third variable to implement swapping/interchanging.

  • Example:
    

  a ← 10
  b ← 20
  
  temp ← a
  a ← b
  b ← temp
  
  or 
  
  temp ← b
  b ← a
  a ← temp
  

3. Exercises

• Practice
• Solution