# String Implementation

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1. Introduction to Characters
2. ASCII Introduction
3. Sum of digits in the string with characters and digits
4. Replace all the characters 'x' with '$'
5. Count uppercase and lower case characters
6. Count number of characters of first string present in the second string

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### Character:
A character represent a single symbol.

There are different types of characters:
* Uppercase characters : ['A' - 'Z']
* Lowercase characters : ['a' - 'z']
* Numeric characters: ['0' - '9']
* Special characters: ['@', '#', '\$', '%', '&'...]

There are a total of 128 characters.

## Syntax

**Example 1:**

char ch = 'a';
System.out.println(ch);

**Output:**

a

**Example 2:**

char ch = 'ab';
System.out.println(ch);

**Output:**

Error: Only a single symbol is a character.

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## Why do we need ASCII Codes?


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## ASCII Codes
ASCII stands for **American Standard Code for Information Interchange.**

These codes are a standardized system of assigning a unique numeric value to each character in the English language and other common characters, such as punctuation marks and symbols.


## Show the ASCII table in the class


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#### Definition
In programming, a string is a data type used to represent a sequence of characters.

#### Syntax
The syntax for declaring and initializing a string variable in Java is:

String str = "Hello World!"; // Double quotes are used to define a string

#### Example -

String str = "How are you?"
print(str) // How are you? will be printed

#### Indexing
String indexing starts from 0, where the first character is at index 0, the second character is at index 1, and so on.

**Example -**

String str = "Hello, World!";
System.out.println(str.charAt(0));   // Output: 'H'
System.out.println(str.charAt(7));   // Output: 'W'

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### Properties of a String
Some of the most commonly used properties of a string include:

* **Length:** The length() method of the String class returns the number of characters in a string. For example,

String str = "Priyanshi";
int n = str1.length(); // assigns 9 to variable n as str has 9 characters.
System.out.println(str.length()); // 9

* **Access a character:** The charAt(index) method of the String class returns the character at that index in a string. Indexing in string is same as that in array and starts from 0. For example,

String str = "Priyanshi";
System.out.println(str.charAt(5)); // output will be 'n'.

* **Iterate a string:** We can iterate over the characters of a string using a loop. One way to do this is to use a for loop that iterates over the index positions of the string, and then use the charAt() method to retrieve the character at each position. For example,

String str = "Priyanshi";
for (int i = 0; i < str.length(); i++) {
    System.out.println(i + " -> " + str.charAt(i));
}

* **Update a string:** In Java, strings are immutable, meaning that their contents cannot be changed after they are created.
* **Concatenating characters to String:** In Java, a character can be concatenated after a string by using the + or += operator, or through the concat() method, defined in the java. lang. String class.

// Concatentaion example

String s1 = "Hello";
String s2 = s1 + "Everyone";
System.out.println(s2); // Output will be "Hello Everyone"


String s3 = "Hi";
s3 = s3 + 'i';
System.out.println(s3); // Output will be "Hii"

s3 = 'e' + s3;
System.out.println(s3); // Output will be "eHii"

s3 = "Bye " + s3; 
System.out.println(s3); // Output will be "Bye eHii"

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#### Problem statement:
Given a string s, you have to find the length of the longest word in the input string.

### Exanple 1:

Input:
hi hello bye

Output:
5

Explanation:
In the sentence "hi hello bye", hello is the longest word, whose length is 5.

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# Question
Given string A, "coding is awesome"
find the length of the longest word in the given string.

# Choices
- [x] 7
- [ ] 6
- [ ] 5
- [ ] I dont know

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### Explanation

In the sentence "coding is awesome", awesome is the longest word, whose length is 7.

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public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String line = scanner.nextLine();
        
        int maxLength = 0;
        int currentLength = 0;

        for (int i = 0; i < line.length(); i++) {
            char currentChar = line.charAt(i);

            if (currentChar != ' ') {
                currentLength++;
            } else {
                if (currentLength > maxLength) {
                    maxLength = currentLength;
                }
                currentLength = 0;
            }
        }

        if (currentLength > maxLength) {
            maxLength = currentLength;
        }
        System.out.println(maxLength);
        scanner.close();
    }

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### Problem
Given a string A of length N and a character B, replace all occurrences of B in string A with character '@'.

**Input Format**

First line is String A
Second line is Character B

**Example:**
abcad
a

**Output:**
@bc@d

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# Question
Given string A,"interviewbit"
String B= "i"
replace all occurrences of B in string A with character '@'.

# Choices
- [x] @nterv@ewb@t
- [ ] i@terv@ewb@t
- [ ] @ntervewb@t
- [ ] I dont know

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### Explanation

Modified string after Replacement of i at 1st, 7th, and 11th position is @nterv@ewb@t

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### Idea:
1. Initialization: Create an empty string result.
2. Iterate: Loop through each character in the input string.
3. Check and Replace: If the current character matches the target character, append '@' to the result; otherwise, append the current character.
4. Final Result: Return the modified string (result).

### Psuedo code

static String replaceCharacter(String str, char targetChar) {
        String result = "";

        for (int i = 0; i < str.length(); i++) {
            char currentChar = str.charAt(i);
            if (currentChar == targetChar) {
                result += '@';
            } else {
                result += currentChar;
            }
        }

        return result;
    }

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### Problem:
Given a string, Count uppercase and lower case characters and print the values.

### Example:
String str="Hello World"

**Output:**
Uppercase: 2
Lowercase: 8

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# Question
Given string ElePHant
Count number of Uppercase character first, then lowercase characters.

# Choices
- [ ] 3 lowercase<br>5 uppercase
- [x] 3 uppercase<br>5 lowercase
- [ ] 5 uppercase<br>9 lowercase
- [ ] I dont know

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public static void main(String args[]) {
        Scanner scn = new Scanner(System.in);
        String str = scn.next();

        int c1 = 0;
        int c2 = 0;

        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);

            if (ch >= 'A' && ch <= 'Z') {
                c1++;
            } else if (ch >= 'a' && ch <= 'z') {
                c2++;
            }
        }

        System.out.println(c1);
        System.out.println(c2);

    }

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### Problem:

Count number of characters of first string present in the second string.

### Example:
String A=abbd
String B=aabb

Output:
Number of common characters: 3(a,b,b)

### Pseudo Code

static int countCommonCharacters(String str1, String str2) {
        int count = 0;

        for (int i = 0; i < str1.length(); i++) {
            char currentChar = str1.charAt(i);

            for (int j = 0; j < str2.length(); j++) {
                if (currentChar == str2.charAt(j)) {
                    count++;
                    break; // Break the inner loop once a common character is found
                }
            }
        }

        return count;
    }

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