pthread in c unexpected declaration speifiers or '...' before '(' - c

Question

here is a snippet of a program I've been working on. Basically, I am getting the same error message twice as described by the title. This is my first time working with pthreads so if someone can tell me what I'm doing wrong I'd appreciate it.
#include <pthread.h>
#include <stdio.h>
void *User_choices();
void *Switch_statement(void *);
void *Server_function(void *);
pthread_t SEND_TO_SERVER_THREAD;
pthread_t PIC_COMMUNICATION_THREAD;
pthread_t USER_INTERFACE_THREAD;
char buf[1024];
void main()
{ // 1
snprintf(buf, 1024, "string");
while(1)
{ // 2
pthread_create(&USER_INTERFACE_THREAD, NULL, User_choices, NULL);
} // 3
} // 4
void *User_choices()
{ // 5
int userinput;
printf("Type 0 to reset sensor, 1 to ping, 2 to receive ADC value, 3 to quit the program: ");
scanf("%i", &userinput);
pthread_create(&PIC_COMMUNICATION_THREAD, NULL, Switch_statement, &userinput);
} // 6
void *Switch_statement((void *)userchoice))
{ // 7
int user = (int)*userchoice;
switch(user)
{ // 8
case 1:
printf("OTHER FUNCTIONS USUALLY GO HERE \n");
break;
case 2: //RETRIEVE ADC CASE
pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buffer);
break;
case 3:
exit(0);
case 0: //RESET CASE
printf("ONCE AGAIN, OTHER FUNCTIONS USUALLY GO HERE");
break; //EXIT THE PROGRAM
default:
printf("Your entry is not a valid option! Try again \n");
} // 9
} // 10
void *Server_function((void *)server_buffer))
{ // 11
const char* send_to_server = (char)*server_buffer;
HTTP_GET(send_to_server);
} // 12
Here are the error codes:
justpthread.c:31:24: error: expected declaration specifiers or ‘...’ before ‘(’ token
void *Switch_statement((void *)userchoice))
^
justpthread.c:53:23: error: expected declaration specifiers or ‘...’ before ‘(’ token
void *Server_function((void *)server_buffer))
If I change just void main to int main, I get the same two error codes. If i take out the parentheses surround (void *), no matter when it's int main or void main, i get the following:
justpthread.c: In function ‘Switch_statement’:
justpthread.c:33:18: warning: dereferencing ‘void *’ pointer [enabled by default]
int user = (int)*userchoice;
^
justpthread.c:33:2: error: invalid use of void expression
int user = (int)*userchoice;
^
justpthread.c:41:76: error: ‘buffer’ undeclared (first use in this function)
pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buffer);
^
justpthread.c:41:76: note: each undeclared identifier is reported only once for each function it appears in
justpthread.c:44:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
exit(0);
^
justpthread.c: In function ‘Server_function’:
justpthread.c:55:37: warning: dereferencing ‘void *’ pointer [enabled by default]
const char* send_to_server = (char)*server_buffer;
^
justpthread.c:55:2: error: invalid use of void expression
const char* send_to_server = (char)*server_buffer;
^
And you guys have me incredibly confused as far as the brackets go, so I numbered all of them. I'm seeing an even number, and they look like they alter directions properly.
Going off of additional recommendations, I changed my code like so:
void main()
{
snprintf(buf, 1024, "string");
while(1)
{
pthread_create(&USER_INTERFACE_THREAD, NULL, User_choices, NULL);
}
}
void *User_choices()
{
int userinput;
printf("Type 0 to reset sensor, 1 to ping, 2 to receive ADC value, 3 to quit the program: ");
scanf("%i", &userinput);
pthread_create(&PIC_COMMUNICATION_THREAD, NULL, Switch_statement, &userinput);
}
void *Switch_statement(void *userchoice)
{
int user = *((int*)userchoice);
switch(user)
{
case 1:
printf("OTHER FUNCTIONS USUALLY GO HERE \n");
break;
case 2: //RETRIEVE ADC CASE
pthread_create(&SEND_TO_SERVER_THREAD, NULL, Server_function, (void *)&buf);
break;
case 0: //RESET CASE
printf("ONCE AGAIN, OTHER FUNCTIONS USUALLY GO HERE");
break; //EXIT THE PROGRAM
default:
printf("Your entry is not a valid option! Try again \n");
}
}
I changed int user... to
int user = *((int*)userchoice);
as recommended, and so I got the following error messages:
justpthread.c: In function ‘Server_function’:
justpthread.c:53:37: warning: dereferencing ‘void *’ pointer [enabled by default]
const char* send_to_server = (char)*server_buffer;
^
justpthread.c:53:2: error: invalid use of void expression
const char* send_to_server = (char)*server_buffer;
So it looks like it got rid of some of the previous errors. So I noticed now that server_buffer is having issues as well so I tried to change that to:
void *Server_function(void *server_buffer)
{
const char* send_to_server = *((char*)server_buffer);
//HTTP_GET(send_to_server);
}
And now I just have one error:
justpthread.c: In function ‘Server_function’:
justpthread.c:53:31: warning: initialization makes pointer from integer without a cast [enabled by default]
const char* send_to_server = *((char*)server_buffer);

Answer 1

For the last warning, you want to cast void* to char*, but with *((char*)server_buffer you are dereferencing pointer to server_buffer and casting void* to char and not to char*.
The proper way is:
const char* send_to_server = (char*)server_buffer;

Answer 2

Remove the (parenthesis) around void * on those lines.

Answer 3

Try void *userchoice and
int user = *((int*)userchoice);
You cannot do anything with void * before you cast it.