Identifying data type of a value in memory in C?

Question

How does a program/application know that the data in a memory address is of a certain data type.

For instance, suppose there is int a; and suppose variable

Answer 1

This information is not stored. For example, you could do things like

int i=15;
char *p=(char*)&i;
char c=*p; //Now, c contain the first byte of 15, which may be 15 or 0

But don't do this unless you really know what do you do. Do stuff like this uncarefully is a common way to errors.