WAP to concatenate two strings

Write a program to concatenate two strings without using string function

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

void concat(char[], char[]);

int main() {
   char s1[50], s2[30];

   printf("Enter String 1: ");
   gets(s1);
   printf("Enter String 2: ");
   gets(s2);

   concat(s1, s2);
   printf("Concatenate string is: %s", s1);

   return (0);
}

void concat(char s1[], char s2[]) {
   int i, j;

   i = strlen(s1);

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

   s1[i] = '\0';
}

Output

Enter String 1: lady
Enter String 2: bird
Concatenate string is: ladybird