Expressions, Variables and Assignments - A Concise and Practical Introduction to Programming Algorithms in Java - page 19

These incrementation instructions are so frequent that they can be ei-
ther written compactly as ++x or x++ (for pre-incrementation and post-
incrementation). Let us explain the difference between pre-incrementation and
post-incrementation :
Consider the following code:

i=2;
j=i++;

This gives the value 3 to i and 2 to j as we do a post-incrementation . That
is, we increment after having evaluated the expression i++ . The above code is
equivalent to:

i=2;
j=i;
i=i+1; // or equivalently i+=1;

Alternatively, consider the pre-incrementation code:
i=2;
j=++i;

This code is equivalent to...
i=2;
i=i+1;
j=i;

... and thus both the values of i and j are equal to 3 in this case. The same
explanations hold for pre-decremention .

Note that technically speaking the ++ syntax can be seen as a unary operator .

i and post-decrementation i −− −−

1.7.3 A calculator for solving quadratic equations

Let us put altogether the use of mathematical functions with variable init ializa-
tions and assignments in a simple program that computes the roots b

√ b 2

− 4 ac
2 a

±

of a quadratic equation ax 2 + bx + c =0:

Program 1.12 A quadratic equation solver
class QuadraticEquationSolver
{ public static void main( String [ ]

arg )

double a,b,c;
a=Math. sqrt (3.0) ;
b=2.0;
c= − 3.0;
double delta=b ∗ b − 4.0 ∗ a ∗ c;
double root1 , root2 ;