C program to convert the contents in a file from lowercase to uppercase and vice versa

Write a C program to convert the contents in a file from lowercase to uppercase and vice versa.

  #include <stdio.h>
  #include <string.h>
  #define MAX 256

  int main() {
        int ch;
        FILE *fp1, *fp2;
        char file1[MAX], file2[MAX];

        /* get the file1 file name from the user */
        printf("Enter your source file name:");
        fgets(file1, MAX, stdin);
        file1[strlen(file1) - 1] = '\0';

        /* get the destination file name from the user */
        printf("Enter your destination file name:");
        fgets(file2, MAX, stdin);
        file2[strlen(file2) - 1] = '\0';

        /* open the first file in read mode */
        fp1 = fopen(file1, "r");

        /* error handling */
        if (!fp1) {
                printf("Unable to open the file %s\n", file1);
                return 0;
        }

        /* open the destination file in write mode */
        fp2 = fopen(file2, "w");

        /* error handling */
        if (!fp2) {
                printf("Unable to open the file %s\n", file2);
                fclose(fp1);
                return 0;
        }

        /* coverts Uppercase to lowercase */

        while (!feof(fp1)) {

                ch = fgetc(fp1);

                if (ch == EOF) {

                        continue;

                } else if (ch >= 'A' && ch <= 'Z') {

                        fputc((ch - 'A' + 'a'), fp2);

                } else if (ch >= 'a' && ch <= 'z') {

                        fputc((ch - 'a' + 'A'), fp2);

                } else {

                        fputc(ch, fp2);

                }

        }

        /* close the opened files */

        fclose(fp1);

        fclose(fp2);

        return 0;

  }

  Output:

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your source file name: data.txt
  Enter your destination file name: output.txt

  jp@jp-VirtualBox:~/$ cat data.txt 
  Apple
  Ball
  Cat
  Donkey
  Elephant
  Fish

  jp@jp-VirtualBox:~/$ cat output.txt 
  aPPLE
  bALL
  cAT
  dONKEY
  eLEPHANT
  fISH

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