String Functions

Overview

String manipulation is tested heavily in interviews (e.g., checking palindromes, finding substrings). The `<string>` library provides robust built-in functions.

Syntax

cpp

#include <string>
using namespace std;

string s = "Hello World";

int len = s.length();       // 11
string sub = s.substr(0, 5); // "Hello" (start, length)
int pos = s.find("World");  // 6 (returns string::npos if not found)

s.replace(6, 5, "C++");     // "Hello C++"
s.erase(5, 4);              // removes characters

Common Pitfalls

Assuming `find()` returns `-1` on failure. It returns `string::npos`, which is a massive unsigned integer.

Interview Tips

When using `find()`, always check the return value against `std::string::npos` to see if the substring was actually found.
Be comfortable using `substr` and `find` to parse sentences into words.

Real-World Example

Extracting a file extension from a filename.

example

cpp

#include <iostream>
#include <string>
using namespace std;

int main() {
    string filename = "report.2023.pdf";
    
    // Find the LAST dot
    size_t dotPos = filename.rfind(".");
    
    if (dotPos != string::npos) {
        string ext = filename.substr(dotPos + 1);
        cout << "Extension: " << ext << endl;
    }
    return 0;
}

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