The language spectrum
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What Is C?C is a programming language. The C language was first developed in 1972 by Dennis Ritchie at AT&T Bell Labs. Ritchie called his newly developed language C simply because there was a B programming language already. (As a matter of fact, the B language led to the development of C.) C is a high-level programming language. In fact, C is one of the most popular general-purpose programming languages. In the computer world, the further a programming language is from the computer architecture, the higher the language's level. You can imagine that the lowest-level languages are machine languages that computers understand directly. The high-level programming languages, on the other hand, are closer to our human languages. (See Figure 1.1.)
High-level programming languages, including C, have the following advantages:
The C language's readability and maintainability benefit directly from its relative closeness to human languages, especially English. Each high-level language needs a compiler or an interpreter to translate instructions written in the high-level programming language into a machine language that a computer can understand and execute. Different machines may need different compilers or interpreters for the same programming language. For instance, I use Microsoft's C compiler to compile the C programs in this book for my personal computer (PC). If I need to run the C programs on a UNIX-based workstation, I have to use another type of C compiler to compile these programs. Therefore, the portability of programs written in C is realized by re-compiling the programs with different compilers for different machines. (See Figure 1.2.) 
Figure 1.2. Porting programs written in C into different types of computers. The Computer's Brain You may know that the brain of a computer is the central processing unit (CPU). Some computers may have more than one CPU inside. A CPU has millions of transistors that make use of electronic switches. The electronic switches have only two states: off and on. (Symbolically, 0 and 1 are used to represent the two states.) Therefore, a computer can only understand instructions consisting of series of 0s and 1s. In other words, machine-readable instructions have to be in binary format. However, a computer program written in a high-level language, such as C, Java, or Perl, is just a text file, consisting of English-like characters and words. We have to use some special programs, called compilers or interpreters, to translate such a program into a machine-readable code. That is, the text format of all instructions written in a high-level language has to be converted into the binary format. The code obtained after the translation is called binary code. Prior to the translation, a program in text format is called source code. The smallest unit of the binary code is called a bit (from binary digit), which can have a value of 0 or 1. 8 bits make up one byte, and half a byte (4 bits) is one nibble. In addition, the C language has other advantages. Programs written in C can be reused. You can save your C programs into a library file and invoke them in your next programming project simply by including the library file. More details on using libraries and invoking C library functions are covered in the rest of this book. C is a relatively small programming language, which makes life easier for you. You don't have to remember many C keywords or commands before you start to write programs in C to solve problems in the real world. For those who seek speed while still keeping the convenience and elegance of a high-level language, the C language is probably the best choice. In fact, C allows you to get control of computer hardware and peripherals. That's why the C language is sometimes called the lowest high-level programming language. Many other high-level languages have been developed based on C. For instance, Perl is a popular programming language in World Wide Web (WWW) design across the Internet. Perl actually borrows a lot of features from C. If you understand C, learning Perl is a snap. Another example is the C++ language, which is simply an expanded version of C, although C++ makes object-oriented programming easier. Also, learning Java becomes much easier if you already know C.
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