How to make a function that satisfies this rule?

If you aren't sure how to do something, try it manually first.
So take a number: 1240012 and think about how you would know that the function should return 0 or 1.

Simple: you look at the number, discard any trailing zeros, and then look for zeros in what is left. When you find one, you look at the next digit.
If that's a zero as well, you return 0.
If it isn't, remember you found one, and keep looking for zeros.
When you get to the end of the number, you check if you found any zeros at all and if so, return 1. Otherwise return 0.

That's pretty simple, isn't it? So now start thinking about ho to implement that in a function. Have a look here: If you are having problems getting started at all, then this may help: How to Write Code to Solve a Problem, A Beginner's Guide[^] and remember that in C you can extract the least significant digit with the modulus operator, and move all the other digits in an integer "down one place" with the divide operator.

Give it a try - it's pretty easy if you think about it for a few minutes.

An alternative approach: convert the number into a string then search for the substring "00" in it (hint: there are standard C functions for such tasks), if the substring is not found then you've just to check for the trailing '0' in order to validate the number.