How do I declare an integer with 30-byte storage capacity?

My question is: I know that the Python language interpreter is made in C. In Python numeric variables do not have size restriction, that is, the more we add value to the variable, the more the variable increases the amount of bytes so that it is holdable to store the value. How do I do in C to declare, for example, variables with 30 bytes in size to store integers or floating numbers?