DSA 100 DAYS OF LEARNING

 

Header Files

• Character Arrays: Typically use <cstring> (or <string.h>).
• std::string: Use <string>.

Examples and Analogous Functions

1. Initialization

Character Array	std::string
char str[] = "Hello";	std::string str = "Hello";

2. Length of the String

Character Array	std::string
Header: <cstring>	Header: <string>
size_t len = strlen(str);	size_t len = str.length();
strlen function is used to get the length.	.length() or .size() member functions.

3. Copying Strings

Character Array	std::string
Header: <cstring>	Header: <string>
char dest[10];	std::string dest;
strcpy(dest, src);	dest = src;
strcpy function is used to copy strings.	Assignment operator (=) is used.

4. Concatenation

Character Array	std::string
Header: <cstring>	Header: <string>
char dest[20] = "Hello ";	std::string dest = "Hello ";
strcat(dest, src);	dest += src;
strcat function is used for concatenation.	+= operator is used for concatenation.

5. Comparison

Character Array	std::string
Header: <cstring>	Header: <string>
if (strcmp(str1, str2) == 0) { /* ... */ }	if (str1 == str2) { /* ... */ }
strcmp function is used for comparison.	Comparison operators (==, !=, <, >, etc.) are used.

6. Input from User

Character Array	std::string
Header: <iostream>	Header: <iostream>, <string>
```cpp	```cpp
char str[50];	std::string str;
std::cin.getline(str, 50);	std::getline(std::cin, str);
```	```
std::cin.getline is used for input.	std::getline is used for input.

Character Array Example

#include <iostream>
#include <cstring>
using namespace std;
int main() {
    char str1[50] = "Hello";
    char str2[50];
    
    // Copying string
    strcpy(str2, str1);
    
    // Concatenation
    strcat(str2, " World");
    
    // Length
    size_t length = strlen(str2);
    
    // Comparison
    if (strcmp(str1, "Hello") == 0) {
        cout << "str1 is equal to 'Hello'" << endl;
    }
    
    // Output
    cout << "str2: " << str2 << endl;
    cout << "Length of str2: " << length << endl;
    
    return 0;
}

std::string Example

#include <iostream>
#include <string>
using namespace std;
int main() {
    string str1 = "Hello";
    string str2;
    
    // Copying string
    str2 = str1;
    
    // Concatenation
    str2 += " World";
    
    // Length
    size_t length = str2.length();
    
    // Comparison
    if (str1 == "Hello") {
        cout << "str1 is equal to 'Hello'" << endl;
    }
    
    // Output
    cout << "str2: " << str2 << endl;
    cout << "Length of str2: " << length << endl;
    
    return 0;
}

#include <iostream>

#include <string>

using namespace std;

int main() {

    // Initialize strings

    string str = "Hello, World!";

    string str2 = "C++ Programming";

    string str3;

    // 1. size() and length()

    cout << "Size of str: " << str.size() << endl;

    cout << "Length of str: " << str.length() << endl;

    // 2. empty()

    cout << "Is str empty? " << (str.empty() ? "Yes" : "No") << endl;

    // 3. clear()

    str3 = str; // Copying str to str3

    str3.clear();

    cout << "str3 after clear(): '" << str3 << "'" << endl;

    // 4. operator= and operator+=

    str = "New String";

    str += " with more text";

    cout << "str after +=: " << str << endl;

    // 5. insert()

    str.insert(4, " inserted");

    cout << "str after insert(): " << str << endl;

    // 6. erase()

    str.erase(4, 9);

    cout << "str after erase(): " << str << endl;

    // 7. replace()

    str.replace(4, 6, "replaced");

    cout << "str after replace(): " << str << endl;

    // 8. substr()

    string sub = str.substr(4, 9);

    cout << "Substring of str: " << sub << endl;

    // 9. find()

    size_t pos = str.find("replaced");

    if (pos != string::npos) {

        cout << "'replaced' found at position: " << pos << endl;

    } else {

        cout << "'replaced' not found" << endl;

    }

    // 10. rfind()

    pos = str.rfind("replaced");

    if (pos != string::npos) {

        cout << "'replaced' found at position (rfind): " << pos << endl;

    } else {

        cout << "'replaced' not found (rfind)" << endl;

    }

    // 11. compare()

    int cmpResult = str.compare(str2);

    if (cmpResult == 0) {

        cout << "str and str2 are equal" << endl;

    } else if (cmpResult < 0) {

        cout << "str is less than str2" << endl;

    } else {

        cout << "str is greater than str2" << endl;

    }

    // 12. c_str()

    cout << "C-style string: " << str.c_str() << endl;

    return 0;

}

            OUTPUT

Size of str: 13

Length of str: 13

Is str empty? No

str3 after clear(): ''

str after +=: New String with more text

str after insert(): New inserted String with more text

str after erase(): New String with more text

str after replace(): New String replaced more text

Substring of str: String rep

'replaced' found at position: 13

'replaced' found at position (rfind): 13

str is less than str2

C-style string: New String replaced more text

Size of str: 13

Length of str: 13

Is str empty? No

str3 after clear(): ''

str after +=: New String with more text

str after insert(): New inserted String with more text

str after erase(): New String with more text

str after replace(): New String replaced more text

Substring of str: String rep

'replaced' found at position: 13

'replaced' found at position (rfind): 13

str is less than str2

C-style string: New String replaced more text

Characteristics of size_t

Unsigned: size_t is always an unsigned type, meaning it can only represent non-negative values.

Common Use Cases:

Representing the size of an object, such as arrays, strings, and memory blocks.

Used by various standard library functions for specifying sizes and counts.