Presenting Choices: Combining Constructs | Year 9 Computing (Cambridge) PDF Download

Introduction to Constructs

In programming, a construct is a basic building block of code. Constructs are used to perform various tasks and can be combined to create complex programs. Common constructs include variables, conditionals, loops, and functions.

Variables

Variables store data that can be used and manipulated throughout a program. For example:
age = 15
name = "Alex"

Conditionals

Conditionals allow the program to make decisions based on certain conditions. The 'if' statement is a basic conditional construct:
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

Loops

Loops are used to repeat a block of code multiple times. The 'for' loop and the 'while' loop are common looping constructs:
for i in range(5):
    print(i)
count = 0
while count < 5:
    print(count)
    count += 1

Functions

Functions are reusable blocks of code that perform a specific task. They can take inputs, called parameters, and return an output:
def greet(name):
    return "Hello, " + name
print(greet("Alex"))

Creating Flowcharts

Flowcharts are visual representations of a program's flow. They use different shapes to represent different constructs and arrows to show the flow of control.

Basic Flowchart Symbols

• Oval: Start or end of the program
• Rectangle: Process or action step
• Diamond: Decision or conditional
• Parallelogram: Input or output

Example Flowchart

Here is an example flowchart for a simple program that checks if a number is even or odd:

• Start: Oval
• Input Number: Parallelogram
• Is Number Even?: Diamond
  • Yes: Print "Even" (Rectangle)
  • No: Print "Odd" (Rectangle)
• End: Oval

Flowcharts help in planning and visualizing the structure of the program before writing the actual code.

Writing and Combining Code Constructs

Combining different constructs allows for more complex and functional programs. Below are examples of how constructs can be combined.

Example 1: Simple Calculator

This program takes two numbers as input and performs basic arithmetic operations based on user choice.

def calculator():
    num1 = float(input("Enter first number: "))
    num2 = float(input("Enter second number: "))
    print("Select operation:")
    print("1. Add")
    print("2. Subtract")
    print("3. Multiply")
    print("4. Divide")
choice = input("Enter choice (1/2/3/4): ")
    if choice == '1':
       print("Result: ", num1 + num2)
    elif choice == '2':
        print("Result: ", num1 - num2)
    elif choice == '3':
        print("Result: ", num1 * num2)
    elif choice == '4':
        if num2 != 0:
          print("Result: ", num1 / num2)
        else:
            print("Error! Division by zero.")
    else:
        print("Invalid input")

Example 2: Grading System

This program assigns grades based on a student's score.
def assign_grade(score):
    if score >= 90:
        return "A"
    elif score >= 80:
       return "B"
    elif score >= 70:
       return "C"
    elif score >= 60:
        return "D"
    else:
        return "F"
score = float(input("Enter your score: "))
print("Your grade is: ", assign_grade(score))
In these examples, we see variables, conditionals, and functions combined to create useful programs.

Conclusion

Understanding and using constructs effectively is fundamental in programming. Constructs like variables, conditionals, loops, and functions form the backbone of any program. Creating flowcharts helps in planning the program structure, and combining constructs allows for the development of complex applications. Practice using these constructs and flowcharts to improve your programming skills.