How to create user defined conditional statements in c?

I have two stacks s1 and s2 with numbers stored in them.

I have a function(say comp) which compares the numerical values of s1 and s2.

I want to know if it is possible to modify the function so that I can use the conditional statements like:

If(s1>s2){statememts}

The naive idea to convert the stacks to their numerical values and then comparing, wont work for me as the stacks contain large numbers(around 30 digits) and the default data type overflows.