Update calculator.c to display full calculation.

[yogirajbshinde21]

In this contribution, I added more descriptive output to the calculation results. Now, the program will display the full calculation entered by the user along with the result. This makes the program more informative and user-friendly. Additionally, I added an extra check to the '%' operator case to prevent division by zero errors.

Pull Request checklist -

• [x] This pull request fixes #issue_reference (Create an issue if not already present.)
• [x] The directory structure is of the form (directory_name) (If directory doesn't exist, create a new.)
• [x] Don't duplicate stuff.

Make sure all the above conditions are met before a PR is created.