1. Introduction to Strings CSIS 1595: Fundamentals of Programming and Problem Solving 1

2. Strings as a Single Value Basic operators: – Assignment: name = “Fred” name1 = name – Comparison: if name == “Fred” if name1 != “Barney” – Concatenation: fullname = name + “ Flintstone” – Repetition: name3 = name * 3

3. String Literals Quotes used to indicate string literal – x is a variable, “x” is a string – 123 is a number, “123” is a string Can use single quote ‘ or double quote “ – x = “Larry” – y = ‘Curley’ – Not z = “Moe’ – Should use one form consistently

4. Escape Characters Syntax: \somecharacter Spacing characters: \t inserts tab \n inserts new line Inserting quotes into strings without having them treated like beginning/end of string literal: \’ inserts single quote \” inserts doule quote Example: print(“He said \”Hello\””)  He said “Hello”

5. Strings as Lists of Characters Strings can be broken down into their individual characters Each character in a string has an index – First index is 0 Helloworld! 01234567891011 index

6. Strings as Lists of Characters Accessing individual characters: Syntax: stringvariable[index] Example: greeting = “Hello world!” print(greeting[7])  ‘r’ Note: Index must be legal print(greeting[12])  error! Can use len function to find length of string len(greeting)  12 – Note: Highest index = length – 1 since first index is 0

7. Strings as Lists of Characters Accessing substring of characters – All characters between start index and end index Syntax: stringvar[start:end] – Example: print(greeting[3:7])  ‘lo wor’ Default syntax: stringvar[start:] – All chars from start to end of string stringvar[:end] – All chars from start of string to end

8. Strings and Loops Loops often used to process strings – Loop counter = index in string Example: Printing all leading substrings of a given word Strategy: – Use stringvar[:end] to print first end characters – Use for loop to vary end from 1 to length of word Use len function to find length of word

9. Strings and Loops

10. For Loops and Strings Special form of for loop for strings for charvariable in stringvariable: – Each time through loop, charvariable is the next character in stringvariable Example: – char = “H” – char = “e” – char = “l” – char = “o” – char = “!”

11. For Loops and Strings Example: “Exploding” a word by inserting a space between each letter Strategy: – Use loop to get each letter – Print it followed by a space (instead of a return)

12. String Mutability Can index be used to change a string? name = “Larry” name[1] = “o”  name now “Lorry” Legal in languages with mutable strings – C, C++,… Not legal in languages with immutable strings – Python, Java,… – Usually related to efficiency of string representation