C Program to Concatenate Two Strings

In this article, you'll learn to easily concatenate two strings without using standard library function strcat().

To understand this example, you should have the knowledge of following C programming topics:

You can concatenate two strings easily using standard library function strcat() but, this program concatenates two strings manually without using strcat() function.

Example: Concatenate Two Strings Without Using strcat()

#include <stdio.h>
int main()
    char s1[100], s2[100], i, j;

    printf("Enter first string: ");
    scanf("%s", s1);

    printf("Enter second string: ");
    scanf("%s", s2);

    // calculate the length of string s1
    // and store it in i
    for(i = 0; s1[i] != '\0'; ++i);

    for(j = 0; s2[j] != '\0'; ++j, ++i)
        s1[i] = s2[j];

    s1[i] = '\0';
    printf("After concatenation: %s", s1);

    return 0;


Enter first string: lol
Enter second string: :)
After concatenation: lol:)