Relational Operators

Objectives

We would like to :

Understand the six relational operators.

Notes

The material for this section is in 2.5.3 of the book.
Remember, part of the syntax for a while loop is while (boolean-expression)
Boolean expressions are expressions that return either true or false.
- remember the boolean type holds either one of these values
- And that true and false are reserved words in java.
- We will take an in depth look at boolean expressions in the future.
- But for now we will stick to the relational operations.
As we saw before i < 4 is a boolean expression
- It is a case of the relational operators.
- It takes two values and returns
  - true if the first is smaller
  - false otherwise.
Relational Operators
- The basic comparison statements.
- <, <=, > >=, ==, !=
- All take two values
- All return a boolean value.
Some cautions
- = and == are different things
  - = is an assignment operator,
    - it copies from the right to the left
  - == is a comparison operator.
  - This does not appear to be a problem in java.
  - while ( i = 3) is a syntax error.
    - error: incompatible types: int cannot be converted to boolean
  - But this is not true in all languages.
- Relational Operators don't work on everything,
  - ```
  String word;
  while ( word < "exit") { 
```
- Produces: bad operand types for binary operator '<'
- == and != work as expected
- Comparison of characters is not as expected.
- Be careful when comparing floats and doubles.
  - == and != can yield unexpected results due to round off error.
  - The other operators are better.
  - Or even
```
double value = 983,
              error;
              
error = Math.abs(value - 0.01);
while (error > 0.01) {
    value = value / 10;
    error = Math.abs(value - 0.01);
    System.out.printf("%.5f %.3E\n", value, error);
} 
```
  - Output:
```
98.30000 9.829E+01
9.83000 9.820E+00
0.98300 9.730E-01
0.09830 8.830E-02
0.00983 1.700E-04 
```
  - Note here we get "close" to the value but not exactly at the value.