myVariable = 57;
is an expression; it evaluates to the value assignedin this case, 57.
Because myVariable = 57 is an expression that evaluates to 57, it can be used as part of another assignment, such as:
mySecondVariable = myVariable = 57;
What happens in this statement is that the literal value 57 is assigned to the variable myVariable. The value of that assignment (57) is then assigned to the second variable, mySecondVariable. Thus, the value 57 is assigned to both variables. You can assign a value to any number of variables with one statement using the assignment operator (=), as in the following:
int a,b,c,d,e; a = b = c = d = e = 20;