Chapter 1 Computers and Programs Almost everyone has used a computer at one time or another.Perhaps you have played computer games or used a computer to write a paper or balance your checkbook.Computers are used to predict the weather, design airplanes,make movies,run businesses,perform financial transactions,and control factories. Have you ever stopped to wonder what exactly a computer is?How can one device perform so many different tasks?These basic questions are the starting point for learning about computers and computer programming. 1.1 The Universal Machine A modern computer might be defined as"a machine that stores and manipulates information under the con- trol of a changeable program."There are two key elements to this definition.The first is that computers are devices for manipulating information.This means that we can put information into a computer,and it can transform the information into new,useful forms,and then output or display the information for our interpretation. Computers are not the only machines that manipulate information.When you use a simple calculator to add up a column of numbers,you are entering information(the numbers)and the calculator is processing the information to compute a running sum which is then displayed.Another simple example is a gas pump.As you fill your tank,the pump uses certain inputs:the current price of gas per gallon and signals from a sensor that reads the rate of gas flowing into your car.The pump transforms this input into information about how much gas you took and how much money you owe. We would not consider either the calculator or the gas pump as full-fledged computers,although modern versions of these devices may actually contain embedded computers.They are different from computers in that they are built to perform a single,specific task.This is where the second part of our definition comes into the picture:computers operate under the control of a changeable program.What exactly does this mean? A computer program is a detailed,step-by-step set of instructions telling a computer exactly what to do. If we change the program,then the computer performs a different sequence of actions,and hence,performs a different task.It is this flexibility that allows your PC to be at one moment a word processor,at the next moment a financial planner,and later on,an arcade game.The machine stays the same,but the program controlling the machine changes. Every computer is just a machine for executing(carrying out)programs.There are many different kinds of computers.You might be familiar with Macintoshes and PCs,but there are literally thousands of other kinds of computers both real and theoretical.One of the remarkable discoveries of computer science is the realization that all of these different computers have the same power;with suitable programming,each computer can basically do all the things that any other computer can do.In this sense,the PC that you might have sitting on your desk is really a universal machine.It can do anything you want it to,provided you can describe the task to be accomplished in sufficient detail.Now that's a powerful machine!Chapter 1 Computers and Programs Almost everyone has used a computer at one time or another. Perhaps you have played computer games or used a computer to write a paper or balance your checkbook. Computers are used to predict the weather, design airplanes, make movies, run businesses, perform financial transactions, and control factories. Have you ever stopped to wonder what exactly a computer is? How can one device perform so many different tasks? These basic questions are the starting point for learning about computers and computer programming. 1.1 The Universal Machine A modern computer might be defined as “a machine that stores and manipulates information under the con￾trol of a changeable program.” There are two key elements to this definition. The first is that computers are devices for manipulating information. This means that we can put information into a computer, and it can transform the information into new, useful forms, and then output or display the information for our interpretation. Computers are not the only machines that manipulate information. When you use a simple calculator to add up a column of numbers, you are entering information (the numbers) and the calculator is processing the information to compute a running sum which is then displayed. Another simple example is a gas pump. As you fill your tank, the pump uses certain inputs: the current price of gas per gallon and signals from a sensor that reads the rate of gas flowing into your car. The pump transforms this input into information about how much gas you took and how much money you owe. We would not consider either the calculator or the gas pump as full-fledged computers, although modern versions of these devices may actually contain embedded computers. They are different from computers in that they are built to perform a single, specific task. This is where the second part of our definition comes into the picture: computers operate under the control of a changeable program. What exactly does this mean? A computer program is a detailed, step-by-step set of instructions telling a computer exactly what to do. If we change the program, then the computer performs a different sequence of actions, and hence, performs a different task. It is this flexibility that allows your PC to be at one moment a word processor, at the next moment a financial planner, and later on, an arcade game. The machine stays the same, but the program controlling the machine changes. Every computer is just a machine for executing (carrying out) programs. There are many different kinds of computers. You might be familiar with Macintoshes and PCs, but there are literally thousands of other kinds of computers both real and theoretical. One of the remarkable discoveries of computer science is the realization that all of these different computers have the same power; with suitable programming, each computer can basically do all the things that any other computer can do. In this sense, the PC that you might have sitting on your desk is really a universal machine. It can do anything you want it to, provided you can describe the task to be accomplished in sufficient detail. Now that’s a powerful machine! 1