ISSUE #49
#### Describe the changes you've made
I have used Regular expressions to validate the user input. If the user enters invalid input, then an error message-box shows up.
#### Describe if there is any unusual behaviour of your code(Write `NA` if there isn't)
NA
#### Additional context (OPTIONAL)
Add any other context or screenshots about the feature request here.
#### Test plan (OPTIONAL)
By entering invalid input such as characters instead of numbers or leaving the fields empty, and then clicking the Calculate button.
#### Checklist
[ ] I have added my name in the contributors list at the end of README.md file.
[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.
[x] The title of my pull request is a short description of the requested changes.
Issue Number 49
fixes #
ISSUE #49 #### Describe the changes you've made I have used Regular expressions to validate the user input. If the user enters invalid input, then an error message-box shows up. #### Describe if there is any unusual behaviour of your code(Write `NA` if there isn't) NA #### Additional context (OPTIONAL) Add any other context or screenshots about the feature request here. #### Test plan (OPTIONAL) By entering invalid input such as characters instead of numbers or leaving the fields empty, and then clicking the Calculate button. #### Checklist