Objective-C 2.0 Data Types

When we look at the different types of software that run on computer systems, from financial applications to graphics intensive games, it is easy to forget that computers are really just binary machines. Binary systems work in terms of 0 and 1, true or false, set and unset. All the data sitting in RAM, stored on disk drives and flowing through circuit boards and buses are nothing more than sequences of 1s and 0s (where each 1 or 0 is referred to as a bit).

Humans, of course, don't think in binary. We work with numbers, letters and words. In order for a human to easily (easily being a relative term in this context) program a computer, some middle ground between human and computer thinking is needed. This is where programming languages such as Objective-C come into play. Programming languages allow us humans to express instructions to a computer in terms and structures we understand, and then compile it down to a format that can be executed by a computer.

One of the fundamentals of any program involves data, and programming languages such as Objective-C define a set of data types that allow us to work with data in a format we understand when writing a computer program. For example, if we want to store a number in an Objective-C program we could do so with the following syntax:

int mynumber = 10;

In the above example, we have created a variable named mynumber of data type integer by using the keyword int. We then assigned the value of 10 to this variable. Once we know that int means we are specifying a variable of integer data type we have an understanding of what is happening in this particular line of an Objective-C program. When we compile the source code down to the machine code used by the CPU, the the number 10 is seen by the computer in binary as:

1010

Similarly, we can express a letter, the visual representation of a digit ('0' through to '9') or punctuation mark (referred to in computer terminology as characters) using the following syntax:

char myletter = 'c';

Once again, this is understandable by a human programmer, but gets compiled down to a binary sequence for the CPU to understand. In this case, the letter 'c' is represented by the decimal number 99 using the ASCII table. When converted to binary, it is stored as:

10101100011

Now that we have a basic understanding of the concept of data types and why they are necessary we can take a closer look at the different data types and qualifiers supported by Objective-C.

int Data Type

The Objective-C int data type can store a positive or negative whole number (in other words a number with no decimal places). The actual size, or range of integer that can be handle by the int data type is machine dependent. typically the amount of storage allocated to int values in either 32-bit or 64-bit depending on the implementation of Objective-C on that platform or the CPU on which the compiler is running.