Input checking for variable types

I have a section of code that needs to work like this in C++.

What it does is take the input from a variable to store it in an integer. What I need to do is check that the input was indeed a number, and not a character or string or double. How do I check that the user input was in the correct format instead of just watching my program crumble?Read the data in as a string, then use strtol or strtoul functions.

Regards,

Paul McKenzie