upper stdin

upper.c

#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <sys/stat.h>
#include <fcntl.h>

#define MAXLINE 4096

int main(int argc, char** argv){
    char line[MAXLINE];
    int n, i, fd;

    while(1) {
        n = read(STDIN_FILENO, line, MAXLINE);
        if(n < 0) {  
            perror("error in read: ");
            return -1;
        }
        printf("n = %d\n", n);
        if(n <= 0){
            printf("break n = %d \n", n); 
            break;
        }
        for(i = 0; i < n; i++){
            line[i] = toupper(line[i]);
        }
        write(STDOUT_FILENO, line, n);
    }
    return 0;
}