Input, Output & String Operations

Input, Output and String Operations

Programs need a conversation with the user

A program is useful when it can accept data, process it, and show a result. Input is data entering the program. At National 5 this usually means data typed using the keyboard. Output is information leaving the program. This is usually text displayed on the screen.

In SQA reference language, input and output have a very specific style. Output uses SEND ... TO DISPLAY. Input uses RECEIVE ... FROM (TYPE) KEYBOARD. The type in brackets matters because it tells the reader what kind of data is expected.

SEND "Enter your age: " TO DISPLAY
RECEIVE age FROM (INTEGER) KEYBOARD
SEND "You are " + age + " years old." TO DISPLAY

Python input and output

Python uses print() for output and input() for keyboard input. The message inside input() is called a prompt. It should be clear enough that the user knows exactly what to type.

name = input("Enter your name: ")
print("Hello " + name)

There is one crucial Python detail: input() always returns a string. Even if the user types 14, Python stores "14" unless you convert it. To do arithmetic, cast the input using int() for whole numbers or float() for decimal numbers.

age = int(input("Enter your age: "))
height = float(input("Enter your height in metres: "))

Using PyCharm for implementation

PyCharm is an Integrated Development Environment, or IDE. It gives you an editor, a run button, error highlighting, and a console in one place. For this course, use one project folder for SDD practice and create one Python file per lesson or task. A sensible file name for this lesson is sdd6_strings.py.

When you create a new PyCharm project, choose a plain Python project, keep the location somewhere you can find again, and make sure a Python interpreter is selected. Then create a new Python file, type your program, and run it using the green Run button or by right-clicking the file and choosing Run. The program output appears in the Run panel at the bottom.

Professional programmers run tiny tests often. Type a few lines, run them, check the output, then continue. This makes mistakes easier to find than writing a whole program before running it for the first time.

Combining text and variables

Output often needs to combine fixed text with variable values. At N5, use + for concatenation in both SQA reference language and Python. In Python, numbers must be converted with str() before they can be joined to text using +:

name = "Sam"
score = 12
print(name + " scored " + str(score) + " points")

For this course, use + when practising concatenation, and convert non-string values with str() first.

String operations

A string is a sequence of characters. Python can measure, transform, and slice strings. len(name) returns the length. name.upper() changes letters to uppercase. name.lower() changes letters to lowercase.

greeting = "hello"
print(greeting.upper())    # HELLO
print(len(greeting))       # 5

Python also lets you access characters by position. The first character is index 0, the second is index 1, and so on. A substring can be taken using slicing, for example code[0:3] gives characters from index 0 up to, but not including, index 3.

code = "N5CS2026"
print(code[0])     # N
print(code[0:4])   # N5CS
print(code[2:6])   # CS20

Exam wording versus Python code

The exam may ask you to read or write SQA reference language, while implementation tasks ask you to write Python. Keep the two styles separate. RECEIVE age FROM (INTEGER) KEYBOARD is the exam design form. age = int(input("Enter age: ")) is the Python implementation. They represent the same idea, but they are not written the same way.