Chapter - 7 Programming Logics & Concepts


Programming Language (Low level, High level, 4 GL)
A vocabulary and set of grammatical rules for instructing a computer to perform specific task is called programming language.
Programming: The process of writing code for computer in order to perform the specific task is called programming.

v Features of a good programming language
·       Integrity: - The calculation used in the program should very accurate.
·        Clarity: - The program should be well readable to aid maintenance.
·       Simplicity: - The program should be able to express the logic in a considerably simple way.
·       Efficiency: - The program should have a good compromise between time and space used.
·       Modularity: - Program should be separated to different logical and self-contained modules.
·       Generality: - The program should be as general as possible within certain limits.
·       Robustness: - Program must be fault-tolerant as much as possible.
      Security: - a program must be secured enough so as to avoid tampering from unwanted people.

Low level Language
Languages that are closer to hardware or machines are called Low Level Language. These languages are machine dependent; they depend upon the internal structure of the machine. There are two types of low level language. They are: -
a) Machine level language b)    Assembly level language
a)    Machine Level Language:-
Machine level language is the language that is directly understood by a computer. In other words, the set of binary digits (0 & 1) is the machine level language. Any information or instructions in this language is represented in terms of 0 & 1. The symbol 0 stands for “off” or the absence of an electric pulse and 1 stands for “on” or the presence of an electric pulse.
Writing a program in a machine level language is a very difficult process. For each instruction different codes are used. The programming codes in a machine language depend upon the hardware of computer. Thus, it is very difficult to write and modify the instructions in a machine level language.

Advantages of machine level language:

1)    It is more efficient than other computer languages.
2)    It is directly understood by computer.
Disadvantages of machine level languages:
1)    Machine languages are machine oriented.
2)    Difficult to write programs and edit.
3)    Time consuming to write programs.


b)    Assembly Level Language: -
The difficulties faced while writing a program in a machine language led to the development of assembly language. It uses symbolic notations to represent the instructions of the machine language. These symbolic notations are called mnemonic codes. For example, ADD for addition, SUB for subtraction etc.
The program written in assembly language is called source program. Source program translated into machine language by a translator program is called object program. Computer viruses are mostly written in Assembly language.
Source Program=>Assembler=>Object Program


Advantages of Assembly Level Language:
1)    Simple to understand and use than machine language.
2)    Easy to write programs.
3)    Easier to debug programs than the programs of machine language.
     Disadvantages to Assembly Level Language:
1)    It is low level language so knowledge of hardware is required.
2)    Programming is a lengthy and time consuming process in assembly level languages.

HIGH LEVEL LANGUAGE:
It is purely problem oriented rather than machine oriented. Easy to define program logic with reference to syntax and extensive vocabularies like English Words. The high-level language code is not directly executable. It requires translators like interpreter or compiler.
The first high level language developed is FORTRAN (in 1956).
Advantages of High Level Language:
  1.     They are machine independent.
  2.     They require less time to write.
  3.     Debugging is easier in high level language.
  4.     Better documentations is provided by high level language

Disadvantages of High Level Language:
  1.   Programs take more time to execute and require more money.
  2.   Programs are not as written in machine level language.
4 GL (4th Generation Language):

Lying above high level languages are called 4 GL. 4 GL is far removed from machine languages and represent the class of computer languages closest to human languages.

Compiler, Interpreter and Assembler                                                                         
  1. a)    Assembler:-
       A program which translates a lower level language program into a machine program is called assembler.
    b)    Compiler:-
A compiler is a program which translates a high level program to machine language at once.
    c)     Interpreter:-Interpreter is a program which translates a statement of high level language program to machine language.

Differences between Compiler and Interpreter
Compiler
Interpreter
1. a compiler is a program which translates a high level program to machine language at once.
1. Interpreter is a program which translates a statement of high level language program to machine language.
2. Program execution time is more before producing executable program.
2. It can execute immediately.
3. It occupies larger part of memory.
3. It occupies less memory space because it is smaller program in comparison to compiler.
4. It is faster because it runs executable programs.
4. It is slower because it repeats the process from the beginning.
5. Examples: C, C++,FORTRAN etc.
5. Examples: BASIC, LISP etc.

List of High Level Language
  1. FORTRAN (Formula Translator)
  2. COBOL (Common Business Oriented Language)
  3. VISUAL BASIC (VB)
  4. JAVA
  5. C: - C was developed by Dennis Ritchie at Bell lab in USA. It has some low level languages features included in it to allow direct control of computer hardware.

Difference between Program and software
Program
Software
1. A collection of instructions that performs certain tasks and is written in the form of computer language is called Program.
1. A set of instruction given to the computer in machine code that tells to the computer what to do and how to perform the given task of the user is called Software.
2. The main objective of program is to make software for general or specific purpose.
2. The main objective of software is to enhance the performance capability of hardware.
3. Examples: - Finding total, percentage, division and result of students in college.
3. Examples:- Windows XP, MS-Excel, MS-Access etc.

Concept of Programming statement
While writing a program, we can use different statements or keywords. Each instructions or statement begins with a reserved word called keywords. Rules of particular keyword must be followed while writing a statement, which is called syntax.

Syntax and Programming Error
If any program contains any mistake due to violation rules of programming language then it is said to be errors or bugs. The process of findings bugs is called debugging. Mainly there are three types of errors in program: syntax Errors, Logical (Semantics) Errors and run-time error.
Syntax Error: -
A syntax error is occurred due to the violation of syntax of a programming language. The key words and the structure of the instructions must be in correct form. A syntax error is very easy to debug because compiler itself detects syntax error and also describes the causes of the errors. So a programmer does not need to trace errors. For Example : if we write the spelling for printf is written pritf , this is a syntax error in C programming.
Logical Error (Semantics error): -
A logical error is occurred due to the violation of semantics of a programming language. It is also called semantics errors. A compiler does not detect the logical errors therefore they are very difficult to find out. The actual output does not come as per the given data therefore; sample data are supplied to the program to examine the logic errors. For example: if we decide to find the rank of student in a test according to their percentages and if two students obtained the same percentage (%) then , there may program get confused and occur a logical error.
Run-time Error:
A run time errors occur during the running time of the software. This kind of error is occurred due to the problem of system or mishandling of the software. Anytime run time error might be occurred so a good programmer has to handle the errors using different error handling mechanism during software development time. For example: Crashing of a program during working on that software is a run time error.

Data type in C language:
The basic element of any program, which describes the nature of variables is called data type .Data types are mainly used to define the type and nature of data such that compiler detects and proceeds.

Data types used in C are as follows:
1.     Int: - int is the keyword for integer. It contains the whole numbers between -32,768 to 32,767. It requires 2 bytes memory and its type specifier is %d.
Examples: - int a=10;
2.     Float: - float is the keyword for floating numbers i.e. decimal numbers. It contains number 3.4e – 38 to 3.4e+38. It requires 4 bytes memory and its type specifier is %f. Example: - float pi=3.14;
3.     Char: - char is the keyword for character. It represents the single alphabet. It requires 1 byte memory and its type specifier is %c. Example: - char choice;
4.     String: - The collection of character is called string. It is enclosed within double quote. Its type specifier is %s. Example: Char str= “Computer”;
# Operator, Operands and Operation:
A symbol that instructs C to perform some operation on one or more operands is called Operator. The data on which operator are performed is called Operand. The result which we obtained after the work is done according to the operator is called Operation.
For example: 
p=3+4; P, 3 and 4 are operands where as = and + are operator and p=7 is the operation.

Program design tools:
Algorithm, Flow chart and Pseudo Code
Planning is the process of finding the steps to solve a problem. It is very important to solve any problem through computer. A planning indicates the direction of flow of the process, accurate calculations, points of decisions and other information in the program. There are three tools of planning to solve problems. They are:

a)     Algorithm: Algorithm can be defined as a sequence of instructions designed in a manner that, if the instructions are executes in the specified sequence, the desired results will be obtained.
Importance / Characteristics of a good algorithm:
·         Each and every instruction should be precise and unambiguous.
·         Each instruction should be performed in a finite time.
·         One or more instructions should not be repeated infinitely.
·         After performing the instruction i.e. after the algorithm terminates, the desired result must be obtained.
Examples of Algorithm:
Q.N. 1) Write an algorithm to read two numbers M and N, add them and print the result.
Solution: To solve the questions
Step 1: Start
Step 2: Read values of two numbers M and N
Step 3: Add M and N
Step 4: Print the sum of M and N
Step 5: Stop

a)      Flow chart:
A flow chart is the diagrammatic or pictorial representation of procedure proposed to solve problem.
Since it charts flow of program, that’s why it is called flow chart.
# Symbols used in flow chart
# Advantages of Flow chart
1.      We can easily find the relationship between each step.
2.      It is easy to communicate with facts of problems.
3.      It is a form of proper program documentation and to modify the programs in future.
4.      With the help of flowchart coding becomes effective and faster.
5.      It is easy to make change to the program and it is easy to debug because flow chart help us to detect, locate and remove logical errors.
# Disadvantages of the Flow Charts
1.      Flow charts are waste of time.
2.      It is slow down process of software development.
3.      It is quite costly to produce and difficult to use and manage.
4.      Flow charts are not meant for man to computer communication.

# Rules for developing Flow chart:
1.      The flow of direction flows from top to bottom or left to right.
2.      All the flow lines must use arrow heads to indicate the flow.
3.      Only one flow line should enter a processing symbol, decision symbol and a terminal symbol.
4.      Flow line should not cross each other.
5.      When drawing flowchart from one page to another the connector symbol should be correctly reformed.

Examples:
Flow chart to calculate sum of M and N

a)    Pseudo code: 
Pseudo-code is a kind of algorithm in which the instructions are expressed in a more English like structure and mathematical expressions. The instructions of pseudo code are similar to the program instructions.
Example of a Pseudo code:
# Pseudo code to calculate sum of M and N
Start
Input M and N
Sum=M+N
Output Sum
Stop

Program Control structures: Sequence, Selection and Iteration:
Sequence:
      A sequential statement control structure is a linear structure. It executes statements one after another in a sequence. There is no mechanism for choosing alternate paths in statement flow. It executes one statement then automatically moves to next statement and so on.

Flowchart of Sequence:

Selection:
The statement which display one statement when the condition is true, otherwise display another statement is known as decision-making statement. Since these statement “control” the flow of execution, they are also known as control statement.
C language has following types of decision making statements are available as follows:
a) Simple if statement
b) if –else statement
c) Nested if-else statement
d) else---if ladder
e) Switch –case statement
Simple if Statement
The general form of a simple if statement is:
      if (test condition)
      {
                  statement-block;
      }
      statement-x;

The ‘statement-block’ may be a single statement or a group of statements. If the test expression is true, the statement block will be executed; otherwise the statement-block will be skipped and the execution will jump to the statement-x. Remember, when the condition is true both the statement block and the statement-x are executed in sequence.






Looping:

The process of executing the same statement repeatedly until a condition is satisfied is called looping. Every loop has three fundamental components: initialization, condition and counter. An initialization statement defines the starting point of the loop. The condition defines the stopping point of the loop and finally the counter counts the number of iterations. The increment and decrement operations are used as counter.
If the task or set of instructions required to be executed “n” number of times, we can use loop statements.
In C- language we have 3 types of looping structures.
1.      For loop
2.     While loop
3.     Do-while loop
 For Loop
The for loop is applied in the situation when you exactly know how many times you want to execute the statements. It is entry-controlled loop.



Exercise:
Explain the types of programming errors with examples.
  1.         What is programming? Differentiate between Compiler and Interpreter.
  2.          What is Programming language? Explain the types of Programming languages      with merits and demerits.
  3.         Differentiate between algorithm and flow chart with suitable examples.
  4.         Draw a flowchart to find the smallest number among any three numbers.
  5.         Define flowchart. Describe the symbols used in flowchart.
  6.         What is an Algorithm? Write an algorithm to compute a sales person’s   commission based on a sales volume shown below:

Sales Amount
Commission(% of sales)
a)       Under Rs. 500
2%
b)       Rs.500 or more but under Rs. 5000
5%
c)       Rs. 5000 and more
10%

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