FILE stream

#include <stdio.h>

int main(){
    FILE *f;
    //neu chon 1

    f=fopen("demo.txt","+a");

    //Neu khong chon lua chon 1 thi dat f=stdout
    f=stdout;
    //khi do 2 lenh sau tuong duong
    printf("1");
    fprintf(f,"1");
    //Co nghia la: fprintf in ra FILE * f,
    //con printf in ra FILE * stdout.
    //khi ta gan f=stdout => fprintf tuong duong lenh printf
}