String Fundamentals

Char Arrays:

• A char array is a sequence of characters stored in contiguous memory locations.
• Char arrays in C/C++ are used to store strings but are not the same as string datatype.

Declaration:

char arr[6] = {'H', 'e', 'l', 'l', 'o', '\0'}; // \0 is the null terminator

Example:

char name[] = "John";  // automatically adds '\0' at the end

• Important Points:
  • A char array must end with the null character \0 to represent a string.
  • If the null terminator is missing, it could lead to undefined behavior when used with string functions.

Accessing and Modifying:

char str[] = "World";
str[0] = 'w';   // Modifies the first character
cout << str;    // Output: world

2. Strings (String Class):

• The string class is part of the C++ Standard Library and provides a more powerful way to handle strings.
• It eliminates the need for manual memory management and provides many useful functions.

Declaration:

string str = "Hello";

Example:

string s1 = "Hello";
string s2 = "World";

// Concatenation
string s3 = s1 + " " + s2;  // "Hello World"

// Accessing elements
cout << s1[0];  // Output: H

3. Difference between Char Arrays and Strings:

Char Array	String Class
Requires manual memory management.	Memory management handled internally.
Functions like strcpy, strlen needed.	Built-in methods like .length(), .substr()
Fixed size once declared.	Dynamic in size.
Example: char arr[5] = "abc";	Example: string s = "abc";

4. Common Operations on Char Arrays:

• strlen(): Returns the length of the string (excluding \0).

char arr[] = "hello";
cout << strlen(arr); // Output: 5

• strcpy(): Copies one string to another.

char src[] = "copy";
char dest[10];
strcpy(dest, src);

• strcmp(): Compares two strings lexicographically

char str1[] = "abc";
char str2[] = "def";
int result = strcmp(str1, str2);  // result < 0 because "abc" < "def"

5. Common String Class Functions:

• .length(): Returns the length of the string

string str = "Hello";
cout << str.length();  // Output: 5

• .substr(start, length): Extracts a substring.

string str = "Hello";
string sub = str.substr(1, 3); // "ell"

• .find(substring): Finds the first occurrence of a substring

string str = "Hello World";
cout << str.find("World");  // Output: 6

6. Converting Between Char Arrays and Strings:

• From char array to string:

char arr[] = "hello";
string str = string(arr); // Conversion to string

• From string to char array

string str = "hello";
char arr[10];
strcpy(arr, str.c_str()); // Converts string to char array

Example of both:

#include <iostream>
#include <cstring>  // For char array functions
#include <string>   // For string class
using namespace std;

int main() {
    // Char Array Example
    char arr[] = "Hello";
    cout << "Char Array Length: " << strlen(arr) << endl;

    // String Example
    string str = "World";
    cout << "String Length: " << str.length() << endl;

    return 0;
}