Like the subscript and dereference operators, assignment returns an lvalue. As such, we can perform multiple assignments in a single expression, provided that each of the operands being assigned is of the same general type:

int ival, jval;  
ival = jval = 0; // ok: each assigned 0 

Unlike the other binary operators, the assignment operators are right associative. We group an expression with multiple assignment operators from right to left. In this expression, the result of the rightmost assignment (i.e., jval) is assigned to ival. The types of the objects in a multiple assignment either must be the same type or of types that can be converted (Section 5.12, p. 178) to one another:

int ival; int *pval;  
ival = pval = 0; // error: cannot assign the value of a pointer to an int  
string s1, s2;  
s1 = s2 = "OK"; // ok: "OK" converted to string 

The first assignment is illegal because ival and pval are objects of different types. It is illegal even though zero happens to be a value that could be assigned to either object. The problem is that the result of the assignment to pval is a value of type int*, which cannot be assigned to an object of type int. On the other hand, the second assignment is fine. The string literal is converted to string, and that string is assigned to s2. The result of that assignment is s2, which is then assigned to s1.