Concatenation without strcat

/*
Write a program in C for concatenation without strcat
*/

#include<stdio.h>

void concatenate_string(char*, char*);

main()
{
char original[100], add[100];

printf("Enter source string\n");
gets(original);

printf("Enter string to concatenate\n");
gets(add);

concatenate_string(original, add);

printf("String after concatenation is \"%s\"\n", original);

return 0;
}

void concatenate_string(char *original, char *add)
{
while(*original)
original++;

while(*add)
{
*original = *add;
add++;
original++;
}
*original = '\0';
}