Module 4: Real Numbers (no more fakes!)

Objectives

By the end of this module, for simple programs with real numbers, you will be able to:

Create variable declarations for variables.
Assign values to variables by simple assignment, and print them out.
Demonstrate ability to perform operations for a desired output.
Evaluate expressions with variables in them.
Convert English descriptions of operations into expressions.
Mentally trace execution with expressions and calculations.
Identify new syntactic elements related to the above.

Real-valued variables

Just like we did with integers, we can declare variables and assign values to them:

Another example:

Again, as with integers, the standard operators apply:

In-Class Exercise 1: Write a program to print out the area of a circle whose radius is 1.5 inches.

In-Class Exercise 2: Can you find a well-known formula or law in science or engineering that uses all four of the standard operators: +, -, *, /? If not, find one that uses as many as possible.

In-Class Exercise 3: Do the increment and decrement operators work with real numbers?

Now consider this simple example:

In-Class Exercise 4: Change the assignment to:

and see what prints. Explain the result.

Casting

Consider the following program:

In-Class Exercise 5: What you suppose will be printed? Try it. Then, change the program so that you initially assign the value of 1 to i and then assign i to x.

An assignment from an int to a double works fine:

About casting:

The assignment from int to double works because every int is a valid double value.
However, a double need not be a valid int.
=> Which is why the compiler complains.
However, we can force an assignment using an explicit cast (jargon alert!)
The result: the largest integer less than the real.
=> The result is 1 above.
An explicit cast is need even if the double's value happens to be an integer like 1.0.
As we'll see later, casting is a general operation that can be applied to different variable types.

In-Class Exercise 6: What do you get when you cast the real value 0.5 to an int?