PROGRAMMING

Programming is, simply, the process of planning the computer solution to a problem. Thus, by writing:

Take the reciprocal of the resistance of all resistors (expressed in ohms); Sum the values obtained in step 1; Take the reciprocal of the sum derived in step 2.

A generalized process or program for finding the total resistance of a parallel resistance circuit has now been derived.

To progress from this example to preparing a program for a computer is not difficult. However, one basic characteristic of the computer must be kept in mind. It cannot think. It can only follow certain commands, and these commands must be correctly expressed and must cover all possibilities. Thus, if a program is to be useful in a computer, it must be broken down into specifically defined operations or steps. Then the instructions, along with other data necessary for performing these operations or steps, must be communicated to the computer in the form of a language or code that is acceptable to the machine. In broad terms, the computer follows certain steps in executing a program. It must first read the instructions (sequentially unless otherwise programmed), and then in accordance with these instructions, it executes the following procedures:

• Locates the parameters (constants) and such other data as may be necessary for problem solution
• Transfers the parameters and data to the point of manipulation
• Manipulates the parameters and data in accordance with certain rules of logic
• Stores the results of such manipulations in a specific location
• Provides the operator (user) with a useful output

Even in a program of elementary character such as the one above, this would involve breaking each of the steps down into a series of machine operations. Then these instructions, parameters, and the data necessary for problem solution must be translated into a language or code that the computer can accept.

Next, we'll provide an introduction to the problem solving concepts and flow charting necessary to develop a program.

OVERVIEW OF PROGRAMMING

Before learning to program in any language, it is helpful to establish some context for the productive part of the entire programming effort. This context comprises the understanding and agreement that there are four fundamental and discrete steps involved in solving a problem on a computer.

The four steps are as follows:

• State, analyze, and define the problem.
• Develop the program logic and prepare a program flowchart or decision table.
• Code the program, prepare the code in machine readable form, prepare test data, and perform debug and test runs.
• Complete the documentation and prepare operator procedures for implementation and production.

Figure 3-2 depicts the evolution of a program. Programming can be complicated, and advance preparation is required before you can actually start to write or code the program. The first two steps, problem understanding/definition and flowcharting, fall into the advance planning phase of programming. It is important at this point to develop correct habits and procedures, since this will prevent later difficulties in program preparation.

Figure 3-2. - Evolution of a program.

Whether you are working with a systems analyst, a customer, or solving a problem of your own, it is extremely important that you have a thorough understanding of the problem.

Every aspect of the problem must be defined:

• What is the problem?
• What information (or data) is needed?
• Where and how will the information be obtained?
• What is the desired output?

Starting with only a portion of the information, or an incomplete definition, will result in having to constantly alter what has been done to accommodate the additional facts as they become available. It is easier and more efficient to begin programming after all of the necessary information is understood. Once you have a thorough understanding of the problem, the next step is flowcharting.

FLOWCHARTING

Flowcharting is one method of pictorially representing a procedural (step-by-step) solution to a problem before you actually start to write the computer instructions required to produce the desired results. Flowcharts use different shaped symbols connected by one-way arrows to represent operations, data flow, equipment, and so forth.

There are two types of flowcharts, system (data) flowcharts and programming flowcharts. A system (data) flowchart defines the major phases of the processing, as well as the various data media used. It shows the relationship of numerous jobs that make up an entire system. In the system (data) flowchart, an entire program run or phase is always represented by a single processing symbol, together with the input/output symbols showing the path of data through a problem solution. For example:

The second type of flowchart, and the one we will talk about in this section is the programming flowchart. It is constructed by the programmer to represent the sequence of operations the computer is to perform to solve a specific problem. It graphically describes what is to take place in the program. It displays specific operations and decisions, and their sequence within the program. For example: