#include <stdio.h>
#include <math.h>
#include <string.h>

int main(void){
	FILE * fp=fopen("data.txt", "wt");
    if(fp==NULL)
    {
        puts("파일오픈 실패!");
        return -1;
    }

    fputc('A', fp);
    fputc('B', fp);
    fputc('C', fp);
    fclose(fp);
    return 0;
	
}