Read first arg argv[1] then convert String in capital letters and then write it in the pipe

I have the following task: Modify the program to take the text from the program as the first argument (argv[1]) is read from the command line and from the child process that from the pipe A read character string in capital letters into which pipe B is written. To convert of a character to a capital letter, the C function toupper() can be used.

argv[1] is working fine, but i failed to convert the argv Text to capital letters. I have the following code:

#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h> 
#include <stdlib.h>
#include <ctype.h>

int main(int argc, char* argv[]) {
  int   n, fd[2], err;
  int   y, fd2[2], err2;
  pid_t pid;
  char writemessages[1][12]={"hello world"};
  char readmessage[12];

  err = pipe(fd);
  if (err < 0) {
    perror("pipe error");
    exit(1);
  }     
  
  err = pipe(fd2);
  if (err < 0) {
    perror("pipe error");
    exit(1);
  }     

  pid = fork();
  if (pid < 0) {
    perror("fork error");
    exit(1);
  }     
  
  else if (pid > 0) {           /* parent */
   close(fd[0]);
   close(fd2[1]);
   printf("Parent Process - Writing to pipe - Message is %s\n", argv[1]);
   write(fd[1], argv[1], sizeof(argv[1]));
   read(fd2[0], readmessage, sizeof(readmessage));
   printf("Parent - Reading from pipe B - Message is %s\n", argv[1]);
   sleep(1); // ps -x
   printf("Child is Terminate!\n");
   wait(0); 
  } 
  else {                        /* child */
   close(fd[1]);
   close(fd2[0]);
     read(fd[0], readmessage, sizeof(readmessage));
   printf("Child Process - Reading from pipe - Message is %s\n", readmessage);
   printf("Sleep 1 Second!\n");
   sleep(1);
   printf("Child Process - Writing to pipe B - Message is %s\n", readmessage);
   write(fd2[1], argv[1], sizeof(argv[1]));
   printf("Child is exit!\n");
   exit(1);
  }
  wait(NULL);
  return 0;
}```