c语言文件，怎么把前面的文件的内容追加搭配后面文件内容

Question

#include<stdio.h>#include<stdlib.h>int main(){ FILE *fp; FILE *fp1; char ch; char ch1; if((fp=fopen("file1.txt","w"))==NULL) {  printf("cannot open this file!\n");  exit(0); }  while((ch=getchar())!='\n')  fputc(ch,fp); fclose(fp);  /*if((fp=fopen("file1.txt","r"))==NULL) {  printf("cannot open this file!\n");  exit(0); } while((ch=fgetc(fp))!=EOF)  putchar(ch); fclose(fp);*/  if((fp1=fopen("file2.txt","w"))==NULL) {  printf("cannot open this file2!\n");  exit(0); }  while((ch1=getchar())!='\n')  fputc(ch1,fp1); fclose(fp1);  /*if((fp1=fopen("file2.txt","r"))==NULL) {  printf("cannot open this file2!\n");  exit(0); }  while((ch1=fgetc(fp))!=EOF)  putchar(ch1); fclose(fp1);*/    return 0;}