1. INTRODUCTION TO PROGRAMMING
Chapter 1
INTRODUCTION TO PROGRAMMING

2. ALGORITHM
An algorithm is defined as the finite set of steps to be followed in order to solve the given problem.
Basically, it gives the set of instructions which must be followed while solving the problem.

3. Example 1:
To find the largest of three numbers. Algorithm: Step 1: Read the three numbers, say A, B
and C. Step 2: If (A>B) and (B<C) then A is the
largest number, go to step 4. Step 3: If (B>A) and (A>C) then B is the
largest else C is the largest
number. Step 4: Stop.

4. Algorithm: Step 1: Read the three test scores, say T1,
Example 2:
To find the average score of a student, for the three test marks (i.e. three subject scores).
Algorithm: Step 1: Read the three test scores, say T1,
T2 and T3. Step 2: SUM = T1+ T2+ T3. Step 3: AVERAGE= SUM/3. Step 4: Display Average Step 5: Stop.

5. Example 3: To find the area of a circle. Algorithm:
Step 1: Read the radius of the circle say r. Step 2: AREA = 3.14 * r * r. Step 3: Display Area. Step 5: Stop.

6. Characteristics of an Algorithm
Input:
An algorithm must be provided with any number of input/data values.
Output:
As we go through the algorithm, step by step, processing statements will yield some result. This enables us to verify the algorithm. Hence at least one output must be produced.

7. Definiteness:
Each statement must be very much clear, and distinct. This ensures that the statements must be unambigious.
Finiteness:
The algorithm must terminate after a finite number of steps.

8. Let us illustrate this point with the help of an example.
Algorithm:
Step 1: Let a = 10. Step 2: If (a>10) then go to step 5. Step 3: X = Y * Z. Step 4: Print X and go to step 2. Step 5: Stop.

9. Let us not bother the purpose of above algorithm, but simply try to trace it. Here we notice that in the algorithm, nowhere the value of ‘a’ is changed, which happens to be controlling the flow and hence never terminates. Such statements must be avoided.
Effectiveness:
It must be possible in practice, to carry out each step manually (using paper and pencil).

10. Example 4
Algorithm for dividing two numbers.
Algorithm:
Step 1: Read the two numbers say a, b.
Step 2: c = a/b.
Step 3: Print c.
Step 4: Stop.

11. Now what happens to this algorithm, if value of b is 0?
Yes, definitely your answer will be “infinite”, right?
Since the system doesn’t give you such answer, hence a care must be taken while you write the algorithm. One way is to provide an appropriate error message, like:

12. Modified Algorithm
Step 1: Read the two numbers say a, b.
Step 2: If (b = 0) then
print “denominator value is 0”
and go to step 5.
Step 3: c = a/ b
Step 4: Print c
Step 5: Stop

13. An algorithm can be expressed in many ways.
One way is to express it in natural language (viz, English).
This way of representation helps to write a program in any language, as it needs only the conversion to respective languages.
Thus it appears more general. However, care must be taken in such case to avoid ambiguity. Another way, is to represent algorithm graphically – a flowchart.

14. Algorithm Design Tools
First write the algorithm for a given problem as if we are solving problem on a paper.
2.Convert each statement of the algorithm into its equivalent program statements and then think of putting the control statement.
We can make use of flowcharts for the algorithm design.

15. Given a list of five numbers find the largest number in the list.
Assignment
Given a list of five numbers find the largest number in the list.

16. Flowchart
It is a diagrammatic way of representing the steps to be followed for solving the given problem.
The main advantage of flowchart is that since it is in the form of diagram one can understand the flow of code very easily. While drawing the flowcharts we make use of certain symbols. These are shown below:

17. Flowchart Notation used
Symbol
Purpose
START/STOP
Assignment
Statements,
Expressions etc.
READ/PRINT

18. Flowchart Notation used
Symbol
Purpose
Decision making
Connector
Flow indication

19. Examples on Flowcharts
Draw a flowchart to add two numbers say ‘a’ and ‘b’. Store the result in sum. Display the Print “sum”.

20. Start
Read numbers
‘a’ and ‘b’
sum = a + b
Print the result
sum
Stop

21. Draw a flowchart to find the factorial of a given number.
Example 2
Draw a flowchart to find the factorial of a given number.

22. Print “factorial of number
Start
Read the number
= number
Yes
If number == 0 No
Print “ factorial for
0 is 1”
Initialize, Fact = 1
i = 1
Stop
Fact = fact * i
i = i +1
Yes
If i<=number
Print “factorial of number
is “fact”
Stop

23. Draw a flow chart to search a number from a given list of n numbers.
Assignment
Draw a flow chart to search a number from a given list of n numbers.

24. Pseudocode
Pseudocode generally does not actually obey the syntax rules of any particular language
There is no systematic standard form, although any particular writer will generally borrow style and syntax for example control structures from some conventional programming language.

25. KEYWORDS
Several keywords are used to indicate common input, output and processing operations:
Input: Read, Obtain, Get
Output: Print, Display, Show
Compute: Compute, Calculate, Determine
Initialize: Set, Init
Add One: Increment, Bump

26. Example 1
Draw the flowchart and also give the pseudocode to calculate the pay
Start
Read hours
Read rate
Pay = hours * rate
End

27. Pseudocode Begin input hours input rate pay = hours * rate print pay
End

28. Assignments
Draw the flowchart and the pseudocode for the following problems:
To find the sum of two numbers.
2.To find the average of three numbers.

29. IF-THEN-ELSE
Binary choice on a given Boolean condition is indicated by the use of four keywords: IF, THEN, ELSE, and ENDIF. The general form is:
IF condition THEN
sequence 1
ELSE
sequence 2
ENDIF
If the condition is true, sequence 1 is performed, otherwise sequence 2 is performed.

30. Example
Draw the flowchart and also give the pseudocode to calculate the pay with overtime
Start
Read hours, rate
Is hours <= 40 No
Yes
Pay = hours * rate
Pay = 40 * rate +
(hours – 40) *1.5 * rate
End

31. Pseudocode Begin input hours, rate if hours <=40 then
pay = hours * rate
else
pay = 40 * rate + (hours –
rate) * 1.5 * rate
endif
print pay
End

32. WHILE
The WHILE is used to specify a loop with a test at the top. The beginning and ending of the loop are indicated by two keywords WHILE and ENDWHILE. The general form is
WHILE condition
sequence
ENDWHILE

33. Example
Draw the flowchart and also give the pseudocode to find the average of 10 numbers.
Start
i=1, sum=0
While i<=10 No
Avg = sum / 10
Yes
Input x
Print avg
sum = x + sum
Increment i
Stop

34. Pseudocode Begin i=1 sum=0 While i <=10 input x sum = sum + x
end while
avg = sum/10
print avg
End

35. CASE
A CASE construct indicates a multiway branch based on conditions that are mutually exclusive. Four keywords, CASE, OF, OTHERS, and ENDCASE, and conditions are used to indicate the various alternatives. The general form is:
CASE expression OF
condition 1 : sequence condition 2 : sequence condition n : sequence n OTHERS: default sequence
ENDCASE

36. Example
CASE  Title  OF                 Mr      : Print "Mister"                 Mrs     : Print "Missus"                 Miss    : Print "Miss"                 Ms      : Print "Mizz"                 Dr      : Print "Doctor" ENDCASE
CASE  grade  OF                 A       : points = 4                 B       : points = 3                 C       : points = 2                 D       : points = 1                 F       : points = 0 ENDCASE

37. REPEAT-UNTIL
This loop is similar to the WHILE loop except that the test is performed at the bottom of the loop instead of at the top. Two keywords, REPEAT and UNTIL are used. The general form is:
REPEAT
sequence
UNTIL condition

38. FOR
This loop is a specialized construct for iterating a specific number of times, often called a “counting” loop. Two keywords, FOR and ENDFOR are used. The general form is:
FOR iteration bounds
sequence
ENDFOR

39. Example
Write a Pseudode to find the average of 10 numbers using FOR loop.
Begin
sum = 0
for i = 1 to 10
input x
sum = sum + x
end for
avg = sum / 10
print avg
End

40. Programming Languages
Computers being electronic brains or having artificial intelligence, it is still necessary for humans to convey this sequence of instructions to the computer before the computer can perform the task.
Programming means designing or creating a set of instructions to ask the computer to carry out certain jobs which normally are very much faster than human beings can do.
In order to do programming, we need to use certain computer language to communicate with the computer.

41. There are many computer languages out there, some of the examples are C, Visual Basic, Fortran, Cobol, Java, C++, Turbo Pascal, Assembly language and etc.
The set of instructions and the order in which they have to be performed is known as an algorithm.

42. The result of expressing the algorithm in a programming language is called a program.
The process of writing the algorithm using a programming language is called programming, and the person doing this is the programmer.

43. Storage
Holds the data that the computer will process and the instructions that indicate what processing is to be done.
In a digital computer, these are stored in a form known as binary, which means that each instruction is represented by a series of bits.

44. Bits are conceptually combined into larger units called bytes (usually 8 bits each) and words (usually 8 to 64 bits each).
Types of Storage device
Registers
Main memory
Secondary storage.

45. Registers
Registers are the fastest and most costly storage units in a computer.
Normally contained within the processing unit
Registers hold data that are involved with the computation currently being performed.

46. Main Memory
Computer Memory is the internal storage areas in the computer.
It comes in the form of chips capable of holding data.
Two Types of Memory
ROM (Read Only Memory)
RAM (Random Access Memory)

47. ROM (READ ONLY MEMORY)
Date is prerecorded for read only, which cannot be removed.
ROM is non-volatile.
Store critical programs such as the program that boots the computer.

48. RAM (RANDOM ACCESS MEMORY)
Date can be read, write and remove in any order.
RAM is volatile.
Caching A small, fast memory system contains the most frequently used words from a slower, larger main memory.

49. Secondary Storage
Secondary storage is the slowest, lowest-cost, and highest-capacity computer storage area.
Programs and data are kept in secondary memory when not in immediate use, so that secondary memory is essentially a long-term storage medium.

50. Machine Language
For the first machines in the 1940s, programmers had no choice but to write in the sequences of digits that the computer executed.
Machine language is a collection of binary digits or bits that the computer reads and interprets. Machine language is the only language a computer is capable of understanding. 

51. Assembly Language
Since each component of a program stands for an object that the programmer understands, using its name rather than numbers should make it easier to program.
By naming all locations with easy-to-remember names, and by using symbolic names for machine instructions, some of the difficulties of machine programming can be eliminated.
A relatively simple program called an assembler converts this symbolic notation into an equivalent machine language program.

52. High Level Language
High Level Languages (HLL) use words similar to English and are easier to write.
The first programming languages were developed in the late 1950s.
If we want to compute |A + B − C|, and store the result in a memory location called D, all we had to do was write D = |A + B − C| and let a computer program, the compiler, convert that into the sequences of numbers that the computer could execute. FORTRAN (an acronym for Formula Translation) was the first major language in this period.

53. Edit-Compile-Link-Execute Process
Developing a program in a compiled language such as C requires at least four steps:
editing (or writing) the program
compiling it
linking it
executing it

54. Editing
Write a computer program with words and symbols that are understandable to human beings.
This is the editing part of the development cycle.
Type the program directly into a window on the screen and save the resulting text as a separate file often called as source file.
Example: The text of a C program is stored with the extension .C.

55. Compiling Cannot execute the source code directly.
Source file must be translated into binary numbers understandable to the computer.
Compiler converts the source file (.c for C) into an object file with the extension .obj.

56. Linking
Many languages come with library routines which can be added to your program.
These routines are written by the manufacturer of the compiler to perform a variety of tasks. So these routines need to be added to your program.
So the linker will convert the file with the extension .obj to a file with the extension .exe (executable file).

57. Executable File Editor produces .c sources files.
The C source file are taken by the complier, which will convert to a file with the extension .obj.
The object file will be taken by the linker, which will convert a file with extension .obj to a file with extension .exe.
Now you can run .exe files simply by typing their names.

58. Loader
Copying a program image from hard disk to the main memory in order to put the program in a ready-to-run state.
Testing
Testing means finding all possible bugs. The program should be tested against all possible inputs.

59. Debugging Documentation
Debugging is the process of analyzing and locating the bugs when software does not behave as expected.
Documentation
Write a brief and accurate comments at the beginning of each function.
It becomes easy for other people unfamiliar with the working of the program.