5: Mainline

C has became popular by virtue of attractive characteristics, such as the following:

• C is easy to learn.
• C programs are fast.
• C programs are concise.
• C compilers—programs that translate C programs into machine instructions—are usually fast and concise.
• C compilers and C programs run on all sorts of computers, from small personal computers to huge supercomputers.
• Unix, a popular operating system, happens to be written in C.