C Program - strcat() Function - How to Concatenate Strings in C

This code combines two input strings entered by the user using the strcat() function from the string.h library. 

#include <stdio.h>
#include <string.h> //strcat() function

int main()
{

    char first_string[100];
    char second_string[100];

    printf("First String: ");
    gets(first_string);

    printf("Second String: ");
    gets(second_string);

    strcat(first_string, second_string);
    printf("Combination: %s \n", first_string);

    return 0;

}

Result: 

First String: some
Second String:  string
Combination: some string

Process returned 0 (0x0)   execution time : 17.672 s
Press any key to continue.

Here's a line-by-line explanation: 

#include <stdio.h>
#include <string.h> //strcat() function

int main()
{

    char first_string[100];
    char second_string[100];

The program includes the necessary header files, and defines two character arrays with a size of 100 each. 

    printf("First String: ");
    gets(first_string);

    printf("Second String: ");
    gets(second_string);

The program prompts the user to enter two strings using printf() function and reads them using the gets() function.

Note: gets() function is considered unsafe and is deprecated in modern C. It is recommended to use fgets() instead. 

    strcat(first_string, second_string);
    printf("Combination: %s \n", first_string);

    return 0;

}

The program uses the strcat() function to concatenate the two strings, storing the result in the first_string variable. The concatenated string is then printed to the console using printf() function. Finally, the program returns 0 to indicate successful completion.