error: too many arguments to function ‘strcasecmp’ "Head First C" - c

Question

I'm trying to get the Internet Knock Knock Protocol Server from O'Reilly's Head First C working but when I try to compile it I receive the following Error.
ikkp_server.c:106:4: error: too many arguments to function ‘strcasecmp’
ikkp_server.c:111:6: error: too many arguments to function ‘strcasecmp’
those lines correspond to the lines,
if(strcasecmp("Who's there?", buf,12))
if(strcasecmp("Oscar who?", buf,10))
The full code is
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
void error(char *msg){
fprintf(stderr, "\n\t\t%s: %s\n\n", msg, strerror(errno));
exit(errno);
}
int catch_signal(int sig, void (*handler)(int)){
struct sigaction action;
action.sa_handler = handler;
sigemptyset(&action.sa_mask);
action.sa_flags = 0;
return sigaction(sig, &action, NULL);
}
int read_in(int socket, char *buf, int len){
char *s = buf;
int slen = len;
int c = recv(socket, s, slen, 0);
while ((c > 0) && (s[c-1] != '\n')){
s += c; slen -= c;
c = recv(socket, s, slen, 0);
}
if ( c < 0)
return c;
else if (c == 0)
buf[0] = '\0';
else
s[c -1] = '\0';
return len - slen;
}
int open_listener_socket(){
int s = socket(PF_INET, SOCK_STREAM, 0);
if (s == -1)
error("Open Socket Error");
return s;
}
void bind_to_port(int socket, int port){
struct sockaddr_in name;
name.sin_family = PF_INET;
name.sin_port = (in_port_t)htons(port);
name.sin_addr.s_addr = htonl(INADDR_ANY);
int reuse = 1;
if(setsockopt(socket, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(int)) == -1)
error("Error reusing socket.");
int c = bind( socket, (struct sockaddr *) &name, sizeof(name));
if (c == -1)
error("Error binding socket.");
}
int say(int socket, char *s){
int result = send(socket, s, strlen(s), 0);
if (result == -1)
error("Can't send message");
return result;
}
int listener_d;
void handle_shutdown(int sig){
if (listener_d)
close(listener_d);
fprintf(stderr, "\n\t\tServer Closed.\n\n");
exit(0);
}
int main(){
//catch sig
if(catch_signal(SIGINT, handle_shutdown) == -1)
error("Signal Error");
//create listener socket..
listener_d = open_listener_socket();
//bind listener.
bind_to_port(listener_d, 3098);
if(listen(listener_d, 10) == -1)
error("Can't Listen.");
struct sockaddr_storage client_addr;
unsigned int address_size = sizeof(client_addr);
puts("Waiting for Connection.");
char buf[255];
while(1){
int connect_d = accept(listener_d, (struct sockaddr *)&client_addr, &address_size);
if( connect_d == -1)
error("Client Connect Error.");
//begin knock knock joke.
if(say(connect_d,"Internet Knock Knock Protocol Server\r\nVersion 1.0\r\n\nKnock! Knock!\r\n" ) != -1){
read_in(connect_d, buf, sizeof(buf));
if(strcasecmp("Who's there?", buf,12))
say(connect_d,"You should say 'Who's there?'\r\n");
else {
if(say(connect_d,"Oscar.") != -1){
read_in(connect_d, buf, sizeof(buf));
if(strcasecmp("Oscar who?", buf,10))
say(connect_d, "You should say 'Oscar who?'\r\n");
else
say(connect_d, "Oscar silly question, get a silly answer!\r\n");
}
}
}
close(connect_d);
}
return 0;
}
man strcasecmp says that it should work?
int strncasecmp(const char *s1, const char *s2, size_t n);
what am I missing?