fill file with user input using posix in c.

fill_file.c

#include <unistd.h>
#include <fcntl.h>
#define size 100

int main() {
    // This program creates a file where it copies the 
    //data read from the keyboard.
    int file, nb_char;
    char buffer[size];
    // create, open file
    file = open("file.txt", O_CREAT | O_WRONLY | O_TRUNC);
    if (file == -1) {
        write(2, "error while opening file.txt \n", 20);
        return -1;
    }

    write(1, "file.txt opened!! \n", 23);
    // get and write user input in file.txt
    while (nb_char = read(0, buffer, size) > 0) {
        if (write(file, buffer, nb_char) == -1) {
            return -1;
        }
    }
    return 0;
}