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String in C++

In competitive programming, programmers use strings or arrays to store and manipulate sequences of characters. This data structure is straightforward, fast, and easy to use.

String implementation in C++

Basic Opeartions

#include <iostream>
#include <string>

using namespace std;

Initialization: Create a string with given value

string s = "hello world";
cout << s;
hello world

Accessing Characters: Access a character by its index (zero-based)

string s = "programming is fun";
cout << "s[0] = " << s[0] << endl;
cout << "s[1] = " << s[5] << endl;
s[0] = p
s[1] = a

Updating Characters: Update a character by its index

string s = "The cat sat on the mat";
cout << "Before: " << s << endl;
s[4] = 'd';
s[5] = 'o';
s[6] = 'g';
s[19] = 'c';
s[21] = 'r';
cout << "After : " << s << endl;
Before: The cat sat on the mat
After : The dog sat on the car

Traversal: Visit all characters of the string

// count vowels in a string
string s = "the cat sat on the mat";
int vowels = 0;
for (int i = 0; i < s.length(); i++) {
    if (s[i] == 'a' || s[i] == 'e' || s[i] == 'i' || s[i] == 'o' || s[i] == 'u') {
        vowels++;
    }
}
cout << "Vowels: " << vowels << endl;
Vowels: 6

Length: Get the number of characters in the string

string s = "the cat sat on the mat";
cout << "Length: " << s.length() << endl;
Length: 22

Reversal: Reverse the order of characters in the string

string s = "the cat sat on the mat";
cout << "Before: " << s << endl;
reverse(begin(s), end(s));
cout << "After : " << s << endl;
Before: the cat sat on the mat
After : tam eht no tas tac eht

Uppercase: Convert all characters in the string to uppercase

string s = "the cat sat on the mat";
cout << "Before: " << s << endl;
for (int i = 0; i < s.length(); i++) {
    s[i] = toupper(s[i]);
}
cout << "After : " << s << endl;
Before: the cat sat on the mat
After : THE CAT SAT ON THE MAT

Lowercase: Convert all characters in the string to lowercase

string s = "THE CAT SAT ON THE MAT";
cout << "Before: " << s << endl;
for (int i = 0; i < s.length(); i++) {
    s[i] = tolower(s[i]);
}
cout << "After : " << s << endl;
Before: THE CAT SAT ON THE MAT
After : the cat sat on the mat

Letters & Numbers: Check if characters in the string are letters or numbers

You can use

  • isalpha() function to check if a character is a letter
  • isdigit() function to check if a character is a number
  • isalnum() function to check if a character is either a decimal digit or an uppercase or lowercase letter.
string s = "I have 2 dogs, a poodle named Max and a German Shepherd named 7h3o#d0r.";

for(int i = 0; i < s.length(); i++) {
    if(isalnum(s[i])) {
        cout << s[i];
    }
}
Ihave2dogsapoodlenamedMaxandaGermanShepherdnamed7h3od0r

🔗 Further Reading