How to append strings using sprintf?

int length = 0;
length += sprintf(Buffer+length, "Hello World");
length += sprintf(Buffer+length, "Good Morning");
length += sprintf(Buffer+length, "Good Afternoon");

Here is a version with some resistance to errors. It is useful if you do not care when errors happen so long as you can continue along your merry way when they do.

int bytes_added( int result_of_sprintf )
{
    return (result_of_sprintf > 0) ? result_of_sprintf : 0;
}

int length = 0;
length += bytes_added(sprintf(Buffer+length, "Hello World"));
length += bytes_added(sprintf(Buffer+length, "Good Morning"));
length += bytes_added(sprintf(Buffer+length, "Good Afternoon"));

You need:

sprintf(Buffer,"Hello World");
sprintf(Buffer + strlen(Buffer),"Good Morning");
sprintf(Buffer + strlen(Buffer),"Good Afternoon");

and of course you need your buffer to be big enough.