C language file reading and writing

#define _CRT_SECURE_NO_WARNINGS
#include <malloc.h>
#include <stdlib.h>  
#include <cstdio>           //FILE The header file 

int main() {
    FILE* fp;        // Define a point FILE Pointer variable of type structure 
    char ch;
    if ((fp = fopen("D:/Cap/test.txt", "w")) == NULL)  // Open the specified file in write only mode , The file address should use /, Otherwise it will be wrong 
    {
        printf("cannot open file\n");
        exit(0);
    }
    ch = getchar();            //fgetc Function brings back a character and assigns it to ch
    while (ch != '#')        // When the input "#" End cycle at 
    {
        fputc(ch, fp);        // Write the read characters to the disk file 
        ch = getchar();        //fgetc Function continues to bring back a character assigned to ch
    }
    fclose(fp);         // Close file 
    return 0;
}