Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 1 ■ Elementary Programming Concepts
• To do accounts, we need an accounting program.
• To learn Spanish, we need a program that teaches Spanish.
• To listen to a CD, we need a music-playing program.
• To send a fax, we need a fax-sending program.
• To use the Internet, we need a program called a “Web browser.”
For every task we want to perform, we need an appropriate program. And in order for the
computer to run a program, the program must be stored (we sometimes say loaded) in the
computer’s memory.
But what is the nature of a program? First, we need to know that computers are built to
execute instructions written in what is called machine language. In machine language, everything
is expressed in terms of the binary number system—1s and 0s. Each computer has its own
machine language and the computer can execute instructions written in that language only.
The instructions themselves are very simple: for example, add or subtract two numbers,
compare one number with another, or copy a number from one place to another. How, then, can
the computer perform such a wide variety of tasks, solving such a wide variety of problems, with
such simple instructions?
The answer is that no matter how complex an activity may seem, it can usually be broken
down into a series of simple steps. It is the ability to analyze a complex problem and express
its solution in terms of simple computer instructions that is one of the hallmarks of a good
programmer.
Machine language is considered a low-level programming language. In the early days of
computing (1940s and ‘50s) programmers had to write programs in machine language, that is,
express all their instructions using 1s and 0s.
To make life a little easier for them, assembly language was developed. This was closely
related to machine language but it allowed the programmer to use mnemonic instruction codes
(such as ADD and names for storage locations (such as sum) rather than strings of binary digits
(bits). For instance, a programmer could refer to a number by sum rather than have to remember
that the number was stored in memory location 1000011101101011.
A program called an assembler is used to convert an assembly language program into
machine language. Still, programming this way had several drawbacks:
• It was very tedious and error prone.
• It forced the programmer to think in terms of the machine rather than in
terms of his problem.
• A program written in the machine language of one computer could not
be run on a computer with a different machine language. Changing your
computer could mean having to rewrite all your programs.
To overcome these problems, high-level or problem-oriented languages were developed in
the late 1950s and ‘60s. The most popular of these were FORTRAN (FORmula TRANslation) and
COBOL (COmmon Business-Oriented Language). FORTRAN was designed for solving scientific
and engineering problems that involved a great deal of numerical computation. COBOL was
designed to solve the data-processing problems of the business community.
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