FILE*fp;
char buff[255];
fp=fopen("plik.txt", "r");
fgets(buff, 255, fp);

int j=buff[0] - '0';
for (int i=0; i<j; i++){
	fgets(buff, 255, fp);
	printf("%s\n, buff);
}
flcose(fp);

fp=open("plik.txt", "a");
scanf("%s", buff);
fputs(buff, fp);
fclose(fp);