fork download

#include <stdio.h>
 
int main(void) 
{
    int status;
    pid_t pid;
 
    printf("A ");
    pid = fork();
    printf("%d ", !pid);
    if (waitpid(-1, &status, 0) > 0) {
	if (WIFEXITED(status) != 0) {
	    printf("%d ", WEXITSTATUS(status));
        }
        exit(0);
    }
 
    printf("B\n");
    exit(1);
}

prog.c: In function 'main':
prog.c:6:5: error: unknown type name 'pid_t'
     pid_t pid;
     ^
prog.c:9:5: warning: implicit declaration of function 'fork' [-Wimplicit-function-declaration]
     pid = fork();
     ^
prog.c:11:5: warning: implicit declaration of function 'waitpid' [-Wimplicit-function-declaration]
     if (waitpid(-1, &status, 0) > 0) {
     ^
prog.c:12:2: warning: implicit declaration of function 'WIFEXITED' [-Wimplicit-function-declaration]
  if (WIFEXITED(status) != 0) {
  ^
prog.c:13:6: warning: implicit declaration of function 'WEXITSTATUS' [-Wimplicit-function-declaration]
      printf("%d ", WEXITSTATUS(status));
      ^
prog.c:15:9: warning: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
         exit(0);
         ^
prog.c:15:9: warning: incompatible implicit declaration of built-in function 'exit'
prog.c:19:5: warning: incompatible implicit declaration of built-in function 'exit'
     exit(1);
     ^

Standard output is empty