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Introduction to Strings

Introduction to Strings. CSIS 1595: Fundamentals of Programming and P roblem Solving 1. Strings as a Single Value. Basic operators: Assignment: name = “Fred” name1 = name Comparison: if name == “Fred” if name1 != “Barney” Concatenation: fullname = name + “ Flintstone”

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Introduction to Strings

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  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 singlequote ‘ or doublequote “ • x = “Larry” • y = ‘Curley’ • Notz = “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 doulequote 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 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 legalprint(greeting[12])  error! • Can use len function to find length of stringlen(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 startindex 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, charvariableis the next character in stringvariable • Example: • char = “H” • char = “e” • char = “l” • 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 mutablestrings • C, C++,… • Not legal in languages with immutablestrings • Python, Java,… • Usually related to efficiency of string representation

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