INTRODUCTION TO PROGRAMMING

INTRODUCTION TO PROGRAMMING

Languages are a means of communication. Normally people interact with each other through a language. On the same pattern, communication with computers is carried out through a language. This language is understood both by user and the machine. The Programming language is the medium of communication between the man and the machine. Programming is a set of instructions given to the computer to perform user defined tasks.

 

PROBLEM SOLVING

Problem solving by the computer involves the following steps.

1)    Problem Definition                  6) Running the program

2)    Analysis                                    7) Debugging

3)    Algorithm                                 8) Testing

4)    Flowchart                                 9) Documentation

5)    Coding

1] PROBLEM DEFINITION

This is the first step in computer problem solving. The problem solver should understand the problem thoroughly in terms of the requirements. That is, what are the input and output operations to be performed ? The programmer should extract from the problem statement, a set of well-defined and precise tasks that can be carried out.

2] ANALYSIS

The given problem must be analyzed before it is solved. This determines the data items, their types and relationship. We should specify the operations (Arithmetic and logic) to be performed on them and checking the suitability in terms of memory and execution time.

3] ALGORITHM

This is a problem solving technique. It can be defined as a step by step procedure to solve a particular problem. It consists of English like statements. Each statement must be precise and well defined to perform a specific operation. When these statements are carried out for a given set of conditions, they will produce the required results. The word algorithm is derived from the famous Arabic author and mathematician, Abu Jafar Mohammad Ibn Musa Al Khowarizmi. The last two terms of the name termed as Algorithm.

CHARACTERISTICS OF ALGORITHM

Each and every algorithm is characterized by the following five important characteristics.

1] Input : It may accept zero or more inputs

2] Outputs : It should produce at least one output (result)

3] Definiteness : Each instruction must be clear, well-defined and precise. There should not be any ambiguity.

4] Finiteness : It should be a sequence of finite instructions. That is, it should end finite time at one or more levels of complexity. It should be effective whenever trace manually for the results.

5] Effectiveness : This means that operations must be simple and are carried out in a finite time at one or more levels of complexity. It should be effective whenever traced manually for the results.

ALGORITHMIC NOTATIONS

While writing algorithms the following notations are considered.

1)        Name of the Algorithm : It specifies the problem to be solved.

2)        Step number : Identification tag of an instruction and it is an unsigned positive integer

3)        Explanatory Comment : It follows the step number and describes the operation.

4)         It should  be written within a pair of square brackets.

5)        Termination : It specifies the end of the algorithm. It is generally a Stop statement and the last instruction in the algorithm.

 

Example 1

Algorithm to compute the area of circle

 

Algorithm : Area of Circle Step 1 : Start

Step 2 : Read radius

Step 3 : [Compute the Area]

Area = 3.142 x radius x radius Step 4 : [Print the Area]

Print “Area of Circle = ”, Area Step 5 : [End of algorithm]

Stop

 

Example 2

Algorithm to calculate the simple interest.

 

Algorithm : Simple Interest Step 1 : Start

Step 2 : [Read the value P, T, R]

Read P, T, R

Step 3 : [Compute the Simple Interest]

SI = ( PxTxR) / 100

Step 4 : [Print the Simple Interest]

Print “Simple Interest= ”, SI Step 5 : [End of algorithm]

Stop

 

Example 3

Algorithm to find the largest of two numbers.

 

Algorithm : Largest of two numbers Step 1 : Start

Step 2 : [Read the values A and B]

Read A, B

Step 3 : [Compare A and B]

If (A>B) Then

Print ‘A is largest’

Else

Print ‘B is largest’

End If

Step 6 : [End of algorithm]

Stop

4] FLOWCHART

This is a chart showing a flow of logic involved in solving a problem. This is defined for an algorithm. The flowchart can be defined as a diagrammatic representation of an algorithm. It is referred to as the blue print of an algorithm. It is also defined as a visual or graphical representation of an algorithm. The flowchart is an easy way to understand and analyze the problem. It is a useful aid for programmers and system analysts.

Flowcharts make use of geometric figures, to specify a particular operation. Those are

 

Geometrical Figure	Name	Function
	Oval	Start and Stop
	Parallelogram	Input and Output
	Rectangle	Processing
	Rhombus	Decision Making
	Arrows	Connections
	Circle	Continuation
	Hexagon	Repetition / Looping

 

Example 1 :     Draw a flowchart to find area of triangle

Example 2 : Draw a flowchart to find the Simple Interest.

 

 

 

5] CODING

 

The complete structure of a problem to be solved by a computer is called a program. The computer does not process an algorithm or a flowchart, but executes the program. A program is a set of instructions to solve a particular problem by the computer and the actual process of writing a program is called coding. Program are written using programming languages and are fed to the computer.

 

6] RUNNING THE PROGRAM :

The program can be run(executed) in the central processing unit. This phase of problem   solving by a computer involves three steps.

1)        Understand the instructions

2)        Store data and instructions

3)        Perform computations

 

The user prepares his/her program and makes it ready for execution. All the instructions stored in the RAM, must be fetched one by one to the ALU to perform corresponding operations. This is called the fetch/execute cycle. The processed data is stored again in the RAM. Finally, they are transferred to the output devices.

 

 

7] DEBUGGING

The process of detecting and correcting errors(mistakes) in the program is known as debugging. There is a program called debugger that takes object program as input and executes it and helps in eliminating the mistakes that occur in the source program.

Generally, programmers commit three types of errors. These are,

1)        Syntax Errors

2)        Logical Errors

3)        Run-time Errors

 

SYNTAX ERRORS

This type of errors is the result of violation of programming rules. On encountering these errors a computer displays error message specifying the line number. It is easy to debug these errors. For Example: If the statement of C is typed without the semicolon at the end, then there will be an error because of a missing semicolon.

 

LOGICAL ERRORS

Logical errors occur during coding process. When the programmer codes his problem, he must take care of correct operations to be performed. The program will be executed but produce some unwanted results. It is very difficult to debug such errors, because the computer does not display them. We can eliminate such errors by tracing it and running for sample data.

 

RUN-TIME ERRORS

These errors occur when we attempt to run an ambiguous instructions. For example, an infinite loop in program sequence which causes no output. These are also occur due to device errors, improper sequencing of constructs, errors in system software, incorrect data input etc., The computer will print error message. Some of run-time errors are:

1)        Divide by zero

2)        Null pointer assignment

3)        Data overflow

 

8] TESTING

The process of executing the program to test the correctness of the outputs of the problem is called testing. The program is tested by executing with different sets of data. Logical errors are the outcome of this process.

 

9] DOCUMENTATIONS

While writing programs, it is good programming practice to make a brief explanatory note on the program or program segments. This explanatory note is called a comment. It explains how the program works and how to interact with it. Thus, it helps other programmers to understand the program.

There are two types of documentation. They are,

1)        Internal documentation

2)        External documentation

 

INTERNAL DOCUMENTATION

This documentation is a comment statement within a program. It describes the function of the program or program segments. These statements are not translated to machine language. Translators simply discard these statements during the translation process.

 

 

EXTERNAL DOCUMENTATION

This documentation is an executable statement in a program. It may be a message to the user to respond to the program requirement. This is accomplished using output statements. It makes the program more attractive and interactive. Some sample examples are given below:

Print, “Input numbers one by one” Print, “Input the order of the matrix” Print, “Do you what to continue ?”