C program to concatenate two strings without using inbuilt functions

PROGRAM:

#include<stdio.h>
void concat(char[],char[]);
int main()
{
    char str[20],str2[20];
    printf("Enter first string\n");
    scanf("%s",str);
    printf("Enter second string\n");
    scanf("%s",str2);
    concat(str,str2);
    return 0;
}
void concat(char s1[],char s2[])
{
    char s3[40];
    int i,k;
    i=k=0;
    while(s1[i]!='\0')
    {
        s3[k]=s1[i];
        i++;
        k++;
    }
    i=0;
    while(s2[i]!='\0')
    {
        s3[k]=s2[i];
        i++;
        k++;
    }
    s3[k]='\0';
    printf("Concatenated string is %s\n",s3);
}

OUTPUT:

Enter first string
Dennis
Enter second string
Ritchie
Concatenated string is DennisRitchie