child-process signal handling in c - c

Question

I need your help in an exercise i have about signal handling between processes. I think that it's a trivial question but i can't find the answer anywhere. I want to print something from the parent in a file, send a signal from the parent to the child, the child has to print in a file and then send a signal from the child to the parent.
The code i am using is this:
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <signal.h>
#include <unistd.h>
#define WRITEF 123451 //Random number
FILE *infile;
void writef() {
fprintf(infile, "Child Starting (%d)\n", getpid());
printf("Child Starting (%d)\n", getpid());
}
int main() {
pid_t pid;
infile = fopen("pid_log.txt","w");
pid = fork();
signal(WRITEF, writef);
if ( pid == 0 ) {
pause();
printf("enter child\n");
}
else {
fprintf(infile, "Parent (%d)\n", getpid());
printf("Parent (%d)\n", getpid());
kill(pid, WRITEF);
pause();
wait((int*)1);
}
fclose(infile);
return 1;
}

Answer 1

PROBLEM SOLVED!!!
The key is that you have to register the signal (use the singal function) before every pause(). Also you cannot use a "user-made" signal and in my case i used SIGCONT.
Here is the final (almost) version of my program:
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <signal.h>
#include <unistd.h>
FILE *infile;
void noth() {
}
void writec() {
infile = fopen("pid_log.txt","a+");
fprintf(infile, "Child (%d)\n", getpid());
printf("Child (%d)\n", getpid());
fclose(infile);
}
void writep() {
infile = fopen("pid_log.txt","a+");
fprintf(infile, "Parent (%d)\n", getpid());
printf("Parent (%d)\n", getpid());
fclose(infile);
}
main() {
pid_t pid = fork();
if ( pid == 0 ) { //child process
signal(SIGCONT,noth); //registering signal before pause()
pause();
infile = fopen("pid_log.txt","a+");
printf("Child Starting (%d)\n",getpid());
fprintf(infile,"Child Starting (%d)\n",getpid());
fclose(infile);
while (1) {
sleep(2);
kill(getppid(), SIGCONT); //sending singal to parent
signal(SIGCONT, writec);
pause();
}
}
else { //parent process
infile = fopen("pid_log.txt","a+");
printf("Parent Starting (%d)\n",getpid());
fprintf(infile,"Parent Starting (%d)\n",getpid());
fclose(infile);
kill(pid, SIGCONT);
signal(SIGCONT, writep);
pause();
while (1) {
sleep(2);
kill(pid, SIGCONT);
signal(SIGCONT, writep);
pause();
}
}
return 1;
}