Programming Techniques

This lesson covers the fundamental programming techniques required by the OCR A-Level Computer Science (H446) specification. These are the building blocks of all programs: sequence, selection, iteration, subroutines, and parameter passing.

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Sequence

Sequence is the most basic programming construct. Instructions are executed one after another, in the order they are written.

# Sequence: each line executes in order
name = input("Enter your name: ")
age = int(input("Enter your age: "))
print(f"Hello {name}, you are {age} years old")

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Selection

Selection allows a program to choose between different paths of execution based on a condition. The condition evaluates to either True or False.

if / elif / else

score = int(input("Enter score: "))

if score >= 90:
    grade = "A*"
elif score >= 80:
    grade = "A"
elif score >= 70:
    grade = "B"
elif score >= 60:
    grade = "C"
elif score >= 50:
    grade = "D"
else:
    grade = "U"

print(f"Grade: {grade}")

Pseudocode

IF score >= 90 THEN
    grade = "A*"
ELSEIF score >= 80 THEN
    grade = "A"
ELSEIF score >= 70 THEN
    grade = "B"
ELSE
    grade = "U"
ENDIF

Switch/Case Statements