C program to concatenate two strings

🧑‍💻 By quescol • 📝 Updated on: 08 May 2025

In this tutorial we are going to learn writing C program to concatenate two given strings. To concatenate we have multiple ways to do.

Here we will see two ways first one using library function strcat() and second one using manually using loop concepts.

How our string concatenate program will work?

• Our program will take two string as an input.
• Now using strcat() function available in string.h header file we can concatenate two string.
• strcat() function takes two string as a parameter and return one string after concatenation.
• We can also concatenate manually by copying one character to another string.

C program to concatenate two strings without using library function strcat

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

int main()
{
    char str1[256], str2[256];
    int i, len;

    printf("=== C Program to Concatenate Two Strings ===\n");

    printf("Enter the first string: ");
    scanf("%s", str1);  // Taking first string input

    printf("Enter the second string: ");
    scanf("%s", str2);  // Taking second string input

    len = strlen(str1); // Find length of first string

    // Concatenate second string to first
    for (i = 0; str2[i] != '\0'; i++) {
        str1[len + i] = str2[i];
    }
    str1[len + i] = '\0'; // Null-terminate the result

    printf("After concatenation the string is: %s\n", str1);

    return 0;
}

Output

=== C Program to Concatenate Two Strings ===
Enter the first string: quescol
Enter the second string: website
After concatenation the string is: quescolwebsite

C program to concatenate two strings using strcat()

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

int main()
{
    char str1[256], str2[256];

    printf("=== C Program to Concatenate Two Strings Using strcat() ===\n");

    printf("Enter the first string: ");
    scanf("%s", str1);  // Taking first string input

    printf("\nEnter the second string: ");
    scanf("%s", str2);  // Taking second string input

    // Using strcat to concatenate str2 to str1
    strcat(str1, str2);

    printf("After concatenation, the string is: %s\n", str1);

    return 0;
}

Output

=== C Program to Concatenate Two Strings Using strcat() ===
Enter the first string: quescol

Enter the second string: website
After concatenation, the string is: quescolwebsite