Concatenation of Two Strings

Last Updated : 31 Oct, 2024

String concatenation is the process of joining two strings end-to-end to form a single string.

Examples

Input: s1 = “Hello”, s2 = “World”
Output: “HelloWorld”
Explanation: Joining “Hello” and “World” results in “HelloWorld”.
Input: s1 = “Good”, s2 = “Morning”
Output: “GoodMorning”
Explanation: Joining “Good” and “Morning” results in “GoodMorning”

Using + Operator

Almost all languages support + operator to concatenate two strings. In C, we have a library function strcat() for the same purpose.

C++

#include <iostream>
#include <string>

using namespace std;

int main() {
    string s1 = "Hello, ";
    string s2 = "World!";
    
    // Concatenating the strings
    string res = s1 + s2;
    
    cout << res << endl;
    return 0;
}

#include <stdio.h>
#include <string.h>

int main() {
    char s1[50] = "Hello, ";
    char s2[] = "World!";
    
    // Concatenating the strings
    strcat(s1, s2);
    
    printf("%s\n", s1);
    return 0;
}

Java

public class GfG {
    public static void main(String[] args) {
        String s1 = "Hello, ";
        String s2 = "World!";
        
        // Concatenating the strings
        String res = s1 + s2;
        
        System.out.println(res);
    }
}

Python

s1 = "Hello, "
s2 = "World!"

# Concatenating the strings
res = s1 + s2

print(res)

using System;

class Program {
    static void Main() {
        string s1 = "Hello, ";
        string s2 = "World!";
        
        // Concatenating the strings
        string res = s1 + s2;
        
        Console.WriteLine(res);
    }
}

JavaScript

let s1 = "Hello, ";
let s2 = "World!";

// Concatenating the strings
let res = s1 + s2;

console.log(res);

Output

Hello, World!

Write your Own Method

Create an empty result string.
Traverse through s1 and append all characters to result.
Traverse through s2 and append all characters to result.

C++

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

string concat(string s1, string s2) {
    string res;
    
    // Append s1 to res
    for (char c : s1) {
        res += c;
    }
    
    // Append s2 to res
    for (char c : s2) {
        res += c;
    }
    
    return res;
}

int main() {
    string s1 = "Hello, ";
    string s2 = "World!";
    
    // Call the function to concatenate the strings
    string res = concat(s1, s2);
    
    cout << res << endl;

    return 0;
}

#include <stdio.h>
#include <string.h>

void concat(const char* s1, const char* s2, char* res) {
    // Append s1 to res
    while (*s1) {
        *res++ = *s1++;
    }
    
    // Append s2 to res
    while (*s2) {
        *res++ = *s2++;
    }
    *res = '\0';
}

int main() {
    const char* s1 = "Hello, ";
    const char* s2 = "World!";
    char res[100];
    
    // Call the function to concatenate the strings
    concat(s1, s2, res);
    
    printf("%s\n", res);
    return 0;
}

Java

import java.util.StringBuilder;

public class Main {
    public static String concat(String s1, String s2) {
        StringBuilder res = new StringBuilder();
        
        // Append s1 to res
        for (char c : s1.toCharArray()) {
            res.append(c);
        }
        
        // Append s2 to res
        for (char c : s2.toCharArray()) {
            res.append(c);
        }
        
        return res.toString();
    }
    
    public static void main(String[] args) {
        String s1 = "Hello, ";
        String s2 = "World!";
        
        // Call the function to concatenate the strings
        String res = concat(s1, s2);
        
        System.out.println(res);
    }
}

Python

def concat(s1, s2):
    res = ''
    
    # Append s1 to res
    for c in s1:
        res += c
    
    # Append s2 to res
    for c in s2:
        res += c
    
    return res

if __name__ == '__main__':
    s1 = 'Hello, '
    s2 = 'World!'
    
    # Call the function to concatenate the strings
    res = concat(s1, s2)
    
    print(res)

using System;

class Program {
    static string Concat(string s1, string s2) {
        string res = "";

        // Append s1 to res
        foreach (char c in s1) {
            res += c;
        }

        // Append s2 to res
        foreach (char c in s2) {
            res += c;
        }

        return res;
    }

    static void Main() {
        string s1 = "Hello, ";
        string s2 = "World!";

        // Call the function to concatenate the strings
        string res = Concat(s1, s2);

        Console.WriteLine(res);
    }
}

JavaScript

function concat(s1, s2) {
    let res = '';
    
    // Append s1 to res
    for (let c of s1) {
        res += c;
    }
    
    // Append s2 to res
    for (let c of s2) {
        res += c;
    }
    
    return res;
}

let s1 = 'Hello, ';
let s2 = 'World!';
let res = concat(s1, s2);
console.log(res);

Output

Hello, World!

Time Complexity : O(m + n) where m and n are lengths of the two strings.

String Problems Topic Wise

kartik

Improve

Article Tags :

Practice Tags :

Concatenation of Two Strings

Using + Operator

Write your Own Method

Similar Reads

Thank You!

What kind of Experience do you want to share?