synchronizing processes with alarms in c - c

Question

I have to write a program about signals and alarms, and i can't use semaphores
A first process (named "B") launches another one (named "A"). "A" have to write random words in a file, once per 5 secs, if it writes the word END terminates the execution. The process "B" have to read the words from the file, if read END then relaunch the process "A". When "B" reads 50 words kills "A" and terminates the execution
The program does not work properly,I think it's because both processes accessing the file at the same time, but I do not know for sure
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#define SECS 5
#define MAX_READ 50
#define MAX_TAM 10
#define N_WORDS 13
int main(void){
int i=0,flag;
pid_t pid;
static char words[][MAX_TAM]={"THE","PROCESS","A","WRITES","IN","A","FILE","WORDS","AND","KILL","ITSELF","WITH","END"};
char *word;
char read[MAX_TAM];
FILE *fp=fopen("file2.txt","w");
if(!fp){
perror("Error opening file");
exit(EXIT_FAILURE);
}
if (signal(SIGALRM, SIG_IGN) == SIG_ERR){
puts("Error");
exit (EXIT_FAILURE);
}
while(1){
flag=0;
switch(pid=fork()){
case -1:
perror("fork error");
exit(EXIT_FAILURE);
case 0: /* A */
srand(getpid());
while(1){
if(alarm(SECS))
pause();
word = words[rand()%N_WORDS];
fprintf(fp,"%s ",word);
printf("A ~ WORD: %s\n",word);
fflush(stdout);
if(!strcmp(word,"END")){
fclose(fp);
printf("ENDING A\n");
exit(EXIT_SUCCESS);
}
}
default: /* Proceso B */
sleep(1);
for( ;i<MAX_READ;i++){
if(alarm(SECS))
pause();
fscanf(fp,"%s",read);
printf("B ~ READING %s\n",read);
fflush(stdout);
if(!strcmp(read,"END")){
flag=1;
break;
}
}
}
if(flag==0)
break;
}
kill(pid,9);
exit(EXIT_SUCCESS);
}