$7\mathrm{.}5$ LAB: Checker for integer string

Forms often allow a user to enter an integer. Write a program that takes in a string representing an integer as every character is a digit $0-9$ or No otherwise.

Ex: If the input is:

$1995$

the output is:

Yes

Ex: If the input is:

$42,000$

or any string with a non$-$integer character, the output is: