String Concatenation in C

Problem Statment: Given two Strings concatenate one string to another and print the result.

Examples:

Example 1:
Input: str1="Take", str2="uforward"
Output: Takeuforward

Example 2:
Input: str1="comp", str2="uter"
Output: computer

Disclaimer: Don’t jump directly to the solution, try it out yourself first.

Solution 1:

The most basic approach would be to reach to the end of the first string. This can be done simply using a for loop or any other loop. Once we reach the end of first string, start traversing the second string and keep appending the elements to the first string.

Note: This would work under the assumption that first string has enough space empty to append the second string.

Pseudo Code:

We take two strings as input.
we declare a variable i = 0 and then run a loop from i =0 until we reach the end of the first string and keep increasing i by 1 in each step.
Now at the end of the loop, i is equal to the length of string + 1
Now we declare another variable j =0 and run a loop from j =0 to the end of the second string.
In each iteration, copy or store the character at jth position in the second string to the ith position of the first string.
Now we print the first string.

Code:

C Program

#include <stdio.h>  
int main()  
{  
    char str1[20]="take";  
    char str2[20]="uforward"; 
    int i=0;  
    
       
    while(str1[i]!='\0')
    {
        i++;
    }
      
    for(int j=0;str2[j]!='\0';j++)  
    {  
        
        str1[i]=str2[j];  
        i++;  
    }  
    str1[i]='\0';  
    printf("After concatenation, the string would look like: %s", str1);  
    return 0;  
}

Output:

After concatenation, the string would look like: takeuforward

Time Complexity: O(m+n), where m is the length of the first string and n is the length of the second string.

Space Complexity: O(1)

Solution 2:

We can also simply use the in-built library function strcat() to concatenate two strings in C.

Syntax: strcat(str1, str2). The concatenated string gets stored in str1.

Code:

C Programs

#include <stdio.h> 
#include<string.h>
int main()  
{  
    char str1[20]="take";  
    char str2[20]="uforward"; 
    strcat(str1,str2);
    printf("After concatenation, the string would look like: %s", str1);  
    return 0;  
}

Output:

After concatenation, the string would look like: takeuforward

Special thanks to Subhrajit Das for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article