4.3 String Iteration

simple for loop to iterate through every character using index with charAt():

String word = "hello";
for (int i = 0; i < word.length(); i++) {
    System.out.println(word.charAt(i));
}

in order to use an enhanced for loop, a character array is needed.
toCharArray() can help accomplish this.
example of iteration with an enhanced for loop:

String word = "hello";
for (char c : word.toCharArray()) {
    System.out.println(c);
}

Popcorn Hack:

Iterate through the characters a string with a while loop

String word = "hello";
int index = 0;

while (index < word.length()) {
    System.out.println(word.charAt(index));
    index++;
}

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What is a substring?

  • a substring is a subset of the main string
  • the substring(a,b) method creates a substring with the characters of the original string with indices of a to b.
  • string.length() returns the length of the string
  • string1.equals(string2) determines if the two strings have the same characters
String word = "sunflower";
String sub = "low";
boolean found = false;
for (int i = 0; i < word.length(); i++) {
    String portion = word.substring(i, i+sub.length());
    if (portion.equals(sub)){
        found = true;
    }
}

System.out.println("is " + )

Iterating through words

use split() to split a string into an array.
then we can iterate through the array to access each individual word

String phrase = "this is a string";
String[] words = phrase.split(" ");
for (String word : words) {
    System.out.println(word);
}

Homework Hack!

code a caesar cipher that will encrypt any string with any key provided.
your code should go into the encrypt() method, and should successfully pass the test cases provided
as a bonus, try to use StringBuilder

public String encrypt() {
    StringBuilder encrypted = new StringBuilder();
    
    for (char c : phrase.toCharArray()) {
        if (Character.isLetter(c)) {
            char base = Character.isUpperCase(c) ? 'D' : 'd';
            char shifted = (char) ((c - base + key) % 26 + base);
            encrypted.append(shifted);
        } else {
            encrypted.append(c);
        }
    }
    
    return encrypted.toString();
}

// it doesnt output anything since it just checks the test cases (outputs a check, meaning it worked!)
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