Procedural Programming (OCR A Level Computer Science)

Procedural Programming

• Procedural programming follows a step-by-step approach to breaking down tasks into routines and subroutines

• It emphasises modular design, where code is grouped into functions and procedures for reuse and clarity

• Variables hold state and control structures that determine the flow of execution in the program

Variables

• Storing data values that can change

x = 10
print(x) # Output: 10

Constants

• Storing values that remain unchanged

PI = 3.1415
print(PI) # Output: 3.1415

Selection

• Decision-making constructs

x = 7
if x > 5:
print("Greater") # Output: Greater
else:
print("Smaller")

Iteration

• Using loops to repeat actions

for i in range(3):
print(i) # Output: 0, 1, 2

Sequence

• Executing statements sequentially

x = 5
y = x + 10
print(y) # Output: 15

Subroutines

• Organising code into reusable parts

def greet(name):
return "Hello, " + name

greeting = greet("Alice")
print(greeting) # Output: Hello, Alice

String Handling

• Operations on character strings

name = "Alice"
upper_name = name.upper()
print(upper_name) # Output: ALICE

File Handling

• Reading from and writing to files

with open('file.txt', 'w') as file:
file.write("Hello, World!")

with open('file.txt', 'r') as file:
content = file.read()
print(content) # Output: Hello, World!

Boolean Operators

• Logical operations

x = 7
y = 5
is_valid = x > 5 and y < 10
print(is_valid) # Output: True

Arithmetic Operators

• Basic mathematical operations

x = 5
y = 3
sum_value = x + y
product = x * y
print(sum_value, product) # Output: 8, 15

Full example

• This script greets the user, asks for two numbers, and multiplies them if they are both greater than 10

• It gives the user three attempts to provide suitable numbers and asks if they want to continue after each attempt. Finally, it writes the greeting and the last multiplication result to a file

# Constants
MAX_ATTEMPTS = 3
FILENAME = 'output.txt'

# Subroutine to greet a user
def greet(name):
    return "Hello, " + name

# Subroutine to multiply two numbers
def multiply(x, y):
    return x * y

# Main program
def main():
    name = input("Please enter your name: ")
    print(greet(name))

    # Iteration to allow multiple attempts
    for attempt in range(MAX_ATTEMPTS):
        x = int(input("Enter the first number: "))
        y = int(input("Enter the second number: "))

        # Selection
        if x > 10 and y > 10:
            result = multiply(x, y)
            print(f"The product of {x} and {y} is {result}")
        else:
            print("Both numbers should be greater than 10.")
            
        # Asking user if they want to continue
        continue_choice = input("Do you want to continue? (y/n): ")
        if continue_choice.lower() != 'y':
            break

    # File Handling
    with open(FILENAME, 'w') as file:
        file.write(greet(name) + "\n")
        file.write(f"Last multiplication result: {result}")

    print(f"Results have been saved to {FILENAME}")

# Sequence: Calling the main program
if __name__ == "__main__":
    main()