what is expression in c code example

Example 1: poiner in c

int c, *pc;

// pc is address but c is not
pc = c; // Error

// &c is address but *pc is not
*pc = &c; // Error

// both &c and pc are addresses
pc = &c;

// both c and *pc values 
*pc = c;

Example 2: what is -> in c

arrow operator ( -> ) in C is used to access a member of a 
struct which is referenced by the pointer in question