祝大家节日快乐 请问一个关于写文件的有关问题

#include  <stdio.h> 
  
 FILE * fp; 
  
 int main(void) 
 {   
 	fp = fopen("fname.txt", "a"); 
 	if (fp == NULL) { 
 		printf("Fail to Open File!\n"); 
 		exit(1); 
 	} 
 	else 
 		fprintf(fp, "%s", "what ever you wanna to input!"); 
  
 	return 0; 
 }