用不同模式的文件进行C编程？

#include<stdio.h>
int main()
{
    FILE *fp;
    char buff[255];

    fp=fopen("test.txt","w");

    printf("File test.txt in w mode\n");
    fprintf(fp,"Template string 1:\n");

    fputs("Template string 2:",fp);
    printf("File test.txt is created at local path\n\n");
    fclose(fp);

    fp=fopen("test.txt","r");
    printf("\n\nFile test.txt in r mode\n");
    fscanf(fp,"%s",buff);
    printf("The content of the file test.txt using fscanf() is:\n%s\n",buff);

    fgets(buff,255,(FILE *)fp);
    printf("The content of the file test.txt using fgets() is :\n%s\n",buff);

    fgets(buff,255,(FILE *)fp);
    printf("The content of the file using fgets() is :\n%s\n",buff);
    fclose(fp);

    fp=fopen("test.txt","a");
    printf("\n\nFile test.txt in a mode\n");
    fprintf(fp,"Template String 3:\n");
    fgets(buff,255,(FILE *)fp);
    printf("After append %s\n",buff);
    fclose(fp);

    fp=fopen("test.txt","r+");
    printf("File test.txt in r+ mode\n");
    fgets(buff,255,(FILE *)fp);
    printf("\n\nThe content of the file test.txt in r+ mode is:\n%s\n",buff);
    fclose(fp);
}
#include<stdio.h>
int main()
{
    FILE *fp;