Strings Chapter Notes | AP Computer Science Principles - Grade 9 PDF Download

Introduction

Strings are an important concept in programming, especially in AP Computer Science Principles. They are used to store and work with text, such as words, sentences, or even single characters. This chapter explains what strings are, how to work with parts of strings using slicing, how to combine strings using concatenation, and key terms related to strings. Understanding strings helps you manipulate text data effectively in your programs.

What Are Strings?

Strings are sequences of characters arranged in a specific order. Similar to lists, you can access individual characters in a string using their index positions. While strings don’t support mathematical operations, they can be manipulated in various ways to suit your needs.

Slicing Strings

A substring is a segment extracted from a larger string. For instance, "APcomputer" is a substring of "APcomputerscienceprinciples." The process of extracting such a segment is called slicing.

Here’s an example of how to slice a string in Python:
string_example1 = "APcomputerscienceprinciples"
print(string_example1[0:10])

This code outputs APcomputer. In Python, indexing starts at 0, and the character at the end index (10) is excluded from the result.

Another example:
string_example2 = "APcomputerscienceprinciples"
print(string_example2[2:9])
 This returns compute, demonstrating how you can extract a different portion of the same string.

Concatenation

Concatenation is the process of combining two or more strings to form a new one. This is typically done using the + operator in Python.

Here’s an example:
part_one = "Hello"
part_two = "_World!"
print(part_one + part_two)

The output will be:
Hello_World!

This shows how two strings can be joined end-to-end to create a single string.

Key Terms

• Concatenation: The act of linking two or more strings together to produce a new, longer string.
• Substring: A smaller sequence of characters taken from a larger string, defined by its start and end positions.