int main() { int sum =0; FILE * ptr; ptr = fopen("d:\\students. "," "); if (ptr ==NULL){ ("file does not exist!!"); exit(0); }

#include <stdio.h>
#include <stdlib.h>

int main() {
    int sum = 0;
    FILE *ptr;
    ptr = fopen("d:\\students.", " ");
    if (ptr == NULL) {
        printf("file does not exist!!");
        exit(0);
    }
}

Explanation: 1. Include necessary libraries: - #include <stdio.h> for standard input-output functions. - #include <stdlib.h> for standard library functions.

1. Declare the main() function of return type int.

2. Declare an integer variable sum and initialize it to 0.

3. Declare a file pointer variable ptr.

4. Use fopen() to open a file named "d:\\students." in the current directory with mode " ". The mode used is empty, which is invalid. It might have been intended to specify a mode like "r" for reading or "w" for writing. There is an extra space after the file name "d:\\students.".

5. Check if the file pointer ptr is NULL, indicating that the file opening failed.

6. If the file pointer is NULL, print a message "file does not exist!!".

7. Exit the program using exit(0) to terminate the program execution.