Data Types

A variable must have a data type like integer, decimal numbers, characters etc. The variable of type Integer stores integers and a character type variable stores characters. The primary difference between data types is their size in memory. Different data types have different size in memory depending on the machine and compilers. These also affect the way they are displayed. The ‘cout’ knows how to display a digit and a character. There are few data types in C language. These data types are reserved words of C language. The reserve words can not be used as a variable name.

Let’s take a look into different data types that the C language provides us to deal with whole numbers, real numbers and character data.

Whole Numbers:
The C language provides three data types to handle whole numbers.

• int
• short
• long

int Data Type:
The data type int is used to store whole numbers (integers). The integer type has a space of 4 bytes (32 bits) in memory. And it is mentioned as ‘int’ which is a reserved word of C, so we can not use it as a variable name.

In programming before using any variable name we have to declare that variable with its data type. If we are using an integer variable named as ‘i’, we have to declare it as

int i ;

The above line is known as declaration statement. When we declare a variable in this way, it reserves some space in memory depending on the size of data type and labels it with the variable name. The declaration statement int i ; reserves 4 bytes of memory and labels it as ‘i’. This happens at the execution time.
Sample Program 1
Let’s consider a simple example to explain int data type. In this example we take two integers, add them and display the answer on the screen.

The code of the program is written below.

The first three lines are the same, we have discussed already in our first program. Now as we need to use variables in our program. So we first declare three variables x, y and z with their data type integer as following.

int x;
int y;
int z;

These three declarations can also be written on one line. C provides us the comma separator (,). The above three lines can be written in a single line as below

int x, y, z;

As we know that semicolon (;) indicates the end of the statement. So we can write many statements on a single line. In this way we can also write the above declarations in the following form

int x; int y; int z;

For good programming practice, write a single statement on a single line.

Now we assign values to variables x and y by using assignment operator. The lines x = 5; and y = 10 assign the values 5 and 10 to the variables x and y, respectively. These statements put the values 5 and 10 to the memory locations labeled as x and y.

The next statement z = x + y; evaluates the expression on right hand side. It takes values stored in variables x and y (which are 5 and 10 respectively), adds them and by using the assignment operator (=), puts the value of the result, which is 15 in this case, to the memory location labeled as z.

Here a thing to be noted is that the values of x and y remains the same after this operation. In arithmetic operations the values of variables used in expression on the right hand side are not affected. They remain the same. But a statement like x = x + 1; is an exceptional case. In this case the value of x is changed.

The next line cout << “ x = “ ; is simple. It just displays ‘ x = ‘ on the screen. Now we want to display the value of x after ‘x =’. For this we write the statement cout << x ; Here comes the affect of data type on cout. The previous statement cout << “x = “ ; has a character string after << sign and cout simply displays the string. In the statement cout << x; there is a variable name x. Now cout will not display ‘x’ but the value of x. The cout interprets that x is a variable of integer type, it goes to the location x in the memory and takes its value and displays it in integer form, on the screen. The next line cout << ”y =”; displays ‘ y = ‘ on the screen. And line cout << y; displays the value of y on the screen. Thus we see that when we write something in quotation marks it is displayed as it is but when we use a variable name it displays the value of the variable not name of the variable. The next two lines cout << “z = x + y = ”; and cout << z; are written to display ‘z = x + y = ’ and the value of z that is 15. Now when we execute the program after compiling, we get the following output

short Data Type:

We noted that the integer has four bytes in memory. So if we have to store a small integer like 5, 10 or 20 it will occupy four bytes. The C provides another data type for storing small whole numbers which is called short. The size of short is two bytes and it can store numbers in range of -32768 to 32767. So if we are going to use a variable for which we know that it will not increase from 32767, for example the age of different people, then we use the data type short for age. We can write the above sample program by using short instead of int.

long Data Type:
stored in int then we use the data type long provided by C. So when we are going to deal with very big whole numbers in our program, we use long data type. We use it in program as:

long x = 300500200;

Real Numbers
The C language provides two data types to deal with real numbers (numbers with decimal points e.g. 1.35, 735.251). The real numbers are also known as floating point numbers.

• float
• double

float Data Type:
To store real numbers, float data type is used. The float data type uses four bytes to store a real number. Here is program that uses float data types.

Here is the output of the above program.

double Data Type:
If we need to store a large real number which cannot be store in four bytes, then we use double data type. Normally the size of double is twice the size of float. In program we use it as:

char Data Type:
So far we have been looking on data types to store numbers, In programming we do need to store characters like a,b,c etc. For storing the character data C language provides char data type. By using char data type we can store characters in variables. While assigning a character value to a char type variable single quotes are used around the character as ‘a’.

The output will be as:

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Data Types

Assignment Operator

The equal-to-sign (=) is used as assignment operator in C language. Do not confuse the algebraic equal-to with the assignment operator. In Algebra X = 2 means the value of X is 2, whereas in C language X = 2 (where X is a variable name) means take the value 2 and put it in the memory location labeled as X, afterwards you can assign some other value to X, for example you can write X = 10, that means now the memory location X contains the value 10 and the previous value 2 is no more there.

Assignment operator is a binary operator (a binary operator has two operands). It must have variable on left hand side and expression (that evaluates to a single value) on right hand side. This operator takes the value on right hand side and stores it to the location labeled as the variable on left hand side, e.g. X = 5, X = 10 + 5, and X = X +1. In C language the statement X = X + 1 means that add 1 to the value of X and then store the result in X variable. If the value of X is 10 then after the execution of this statement the value of X becomes 11. This is a common practice for incrementing the value of the variable by one in C language. Similarly you can use the statement X = X - 1 for decrementing the value of the variable by one. The statement X = X + 1 in algebra is not valid except when X is infinity. So do not confuse assignment operator (=) with equal sign (=) in algebra. Remember that assignment operator must have a variable name on left hand side unlike algebra in which you can use expression on both sides of equal sign (=). For example, in algebra, X +5 = Y + 7 is correct but incorrect in C language. The compiler will not understand it and will give error.

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Assignment Operator

Variables

We store every kind of data in variables. Variables are locations in memory for storing data. The memory is divided into blocks. It can be viewed as pigeon-holes. You can think of it as PO Boxes also. In post offices there are different boxes and each has an address. Similarly in memory, there is a numerical address for each location of memory (block). It is difficult for us to handle these numerical addresses in our programs. So we give a name to these locations. These names are variables. We call them variables because they can contain different values at different times.

The variable names in C may be started with a character or an underscore ( _ ). But avoid starting a name with underscore ( _ ). C has many libraries which contain variables and function names normally starting with underscore ( _ ). So your variable name starting with underscore ( _ ) may conflict with these variables or function names.

In a program every variable has:

• Name
• Type
• Size
• Value

The variables having a name, type and size (type and size will be discussed later) are just empty boxes. They are useless until we put some value in them. To put some value in these boxes is known as assigning values to variables. In C language, we use assignment operator for this purpose.

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Variables

Our First Program,c++ First program

Let’s write our first program in C and understand the basics of C program by explaining it line by line.

# include

main()

{
cout << "hello!"; }

The first line is # include

This is preprocessor directive. The features of preprocessor will be discussed later. For the time being take this line on faith. You have to write this line. The sign # is known as HASH and also called SHARP.

The next line contains main().

There is a main() in every C program. It occurs once in a program. When we write a program and it compiles successfully, it converts into an executable program (file). Then we execute it by typing the command or by double clicking in graphical interface. The system then loads the program into memory. Now the question arises from where the execution should start. In C programs the execution always starts from the main(). In large programs there may be many modules. But the starting point of the program will always be the main function.

Notice that there are parentheses (“( )”, normal brackets) with main. Here the parentheses contain nothing. There may be something written inside the parentheses. It will be discussed in next lectures.

Next, there is a curly bracket also called braces("{ }"). Here is a thing to remember that brackets (parentheses ( ) and braces { }) always occur in pairs. The body of main is enclosed in braces. Braces are very important in C; they enclose the blocks of the program.

The next line in the program,

cout << “hello!”;

is a statement in C language. There are many things in this line to be discussed. Let’s see them one by one.

The word ‘cout’ is known as stream in C and C++. Stream is a complicated thing, you will learn about it later. Think a stream as a door. The data is transferred through stream, cout takes data from computer and sends it to the output that is the screen of the monitor. So we use cout for output.

The sign << indicates the direction of data. Here it is towards cout and the function of cout is to show data on the screen. The thing between the double quoutes (“ ”) is known as character string. In C programming character strings are written in double quotes. Whatever will be written in quotation marks the sign << will direct it towards cout which will show it on the screen. There is a semicolon (;) at the end of the statement. This is very important. All C statements end with semicolon (;). Missing of a semicolon (;) at the end of statement is a syntax error and compiler will report an error during compilation. The only semicolon (;) on a line is a null statement. It does nothing. The extra semicolons may be put at the end but are useless and aimless. Do not put semicolon (;) at a wrong place, it may cause a problem during the execution of the program or may cause a logical error. In this program we give a fixed character string to cout and the program prints it to the screen as: hello!

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Our First Program,c++ First program

IDE (Integrated Development Environment)

There are many IDEs provided by different vendors. These IDEs contain editor, compilers, debugger, linker and loader. The benefit of an IDE is that we have all these things at the same place. We write program, compile it and run it at the same place (i.e. in an IDE). But the difficulty is that in an IDE the things become complex. There are many buttons/menus provided to perform different tasks. We have to take care of all aspects while working in an IDE. The IDE we are going to use in our course is Dev C++, which is a product of Bloodshed Software and is available on the internet for free down load at the site (http://www.bloodshed.net).

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IDE (Integrated Development Environment)

Steps involved in writing and executing a program

The following figure represents a graphical explanation of all the steps involved in
writing and executing a program.

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Steps involved in writing and executing a program

Tools Of Trade

As programmer we need different tools to develop a program. These tools are needed for the life cycle of programs.
editors:
First of all we need a tool for writing the code of a program. For this purpose we used Editors in which we write our code. We can use word processor too for this, but word processors have many other features like bold the text, italic, coloring the text etc, so when we save a file written in a word processor, lot of other information including the text is saved on the disk. For programming purposes we don’t need these things we only need simple text. Text editors are such editors which save only the text which we type. So for programming we will be using a text editor.
Compiler and Interpreter:
As we write the code in English and we know that computers can understand only 0s and 1s. So we need a translator which translates the code of our program into machine language. There are two kinds of translators which are known as Interpreter and Compilers. These translators translate our program which is written in C-Language into Machine language. Interpreters translates the program line by line meaning it reads one line of program and translates it, then it reads second line, translate it and so on. The benefit of it is that we get the errors as we go along and it is very easy to correct the errors. The drawback of the interpreter is that the program executes slowly as the interpreter translates the program line by line. Another drawback is that as interpreters are reading the program line by line so they cannot get the overall picture of the program hence cannot optimize the program making it efficient.
Compilers also translate the English like language (Code written in C) into a language (Machine language) which computers can understand. The Compiler read the whole program and translates it into machine language completely. The difference between interpreter and compiler is that compiler will stop translating if it finds an error and there will be no executable code generated whereas Interpreter will execute all the lines before error and will stop at the line which contains the error. So Compiler needs syntactically correct program to produce an executable code. We will be using compiler in our course.
Debugger:
Another important tool is Debugger. Every programmer should be familiar with it. Debugger is used to debug the program i.e. to correct the logical errors. Using debugger we can control our program while it is running. We can stop the execution of our program at some point and can check the values in different variables, can change these values etc. In this way we can trace the logical errors in our program and can see whether our program is producing the correct results. This tool is very powerful, so it is complex too.
Linker:
Most of the time our program is using different routines and functions. So our program standalone cannot be executed, it also needs the executable code of those routines/functions which we are using in our program. Linker is a tool which performs this job, it checks our program and includes all those routines or functions which we are using in our program to make a standalone executable code and this process is called Linking.
Loader:
After a executable program is linked and saved on the disk and it is ready for
execution. We need another process which loads the program into memory and then
instruct the processor to start the execution of the program from the first instruction (the starting point of every C program is from the main function). This processor is known as loader. Linker and loaders are the part of development environment. These are part of system software.

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Tools Of Trade

History of C Language

The C language was developed in late 60’s and early 70’s, in Bell Laboratories. In those days BCPL and B languages were developed at Bell Laboratories. The BCPL language was developed in 1967 by Martin Richards as a language for writing operating systems software and compilers. In 1970 Ken Thompson used B language to create early versions of the UNIX operating system at Bell Laboratories. Thus both the languages were being used to develop various system software even compilers. Both BCPL and B were ‘type less’ languages, every data item occupied one ‘word’ in memory and the burden of treating a data item as a whole number or real number, for example was the responsibility of the programmer.

Dennis Ritchie developed a general purpose language, called C language, by using different features of BCPL and B languages. C uses many important concepts of BCPL and B while adding data typing and other features. In the start C became widely known as the development language of the UNIX operating system, and the UNIX operating system was written by using this C language. The C language is so powerful that the compiler of C and other various operating systems are written in C. C language has almost unlimited powers to do with computers. You can program to turn on or off any device of computer. You can do a lot to hard disk and other peripherals. It is very easy to write a program in C that stops the running of computer. So be careful while programming in C.

The C language and UNIX operating system widely spread in educational and research institutions. There was C and UNIX everywhere. Due to the wide spread of C, different researchers started to add their features in the language. And thus different variations in C came into existence. Many universities developed their own C by adding different features to the C language developed by Ritchie. These variations led to the need of a standard version of C. In 1983 a technical committee was created under the American National Standards Committee on Computer and Information Processing to provide an unambiguous and machine-independent definition of the language. In 1989 the standard was approved. ANSI cooperated with the International Standard Organization (ISO) to standardize C worldwide.

There were revolutions in computer industry, there came new features and languages. So immediately after C came the C++. Stroustrup wrote the C++. First its name was ‘C with objects’ and then eventually became C++. It is an object oriented language having all powers of C. The development environment which we are going to use for programming is actually the environment of C++. It has objects, methods and many others thing. But we will avoid object oriented features in our course.

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types of system softwares

o Operating system
o Device drivers
o Utilities

Operating system:
An operating system (sometimes abbreviated as "OS") is the program that manages all the other programs in a computer. It is a integrated collection of routines that service the sequencing and processing of programs by a computer. Note: An operating system may provide many services, such as resource allocation, scheduling, input/output control, and data management.
Definition of Operating system:
“Operating system is the software responsible for controlling the allocation and usage of hardware sources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The operating system is the foundation on which applications, such as word processing and spreadsheet programs, are built. (Microsoft)”

Device drivers:
The device driver software is used to communicate between the devices and the computer. We have monitor, keyboard and mouse attached to almost all PC’s; if we look at the properties of these devices we will see that the operating system has
installed special software to control these devices. This piece of software is called device driver software. When we attach a new device with the computer, we need software to communicate with this device. These kinds of software are known as device drivers e.g. CD Rom driver, Sound Card driver and Modem driver. Normally manufacturer of the device provide the device driver software with the device. For scanners to work properly with the computers we install the device driver of the scanner. Nowadays if you have seen a scanner, it comes with TWAIN Drivers. TWAIN stands for Technology Without An Interesting Name.

Utility Software:
Utility software is a program that performs a very specific task, usually related to managing system resources. You would have noticed a utility of Disk Compression. Whenever you write a file and save it to the disk, Compression Utility compresses the file (reduce the file size) and write it to the disk and when you request this file from the disk, the compression utility uncompressed the file and shows its contents. Similarly there is another utility, Disk Defragmentation which is used to defragment the disk. The data is stored on the disks in chunks, so if we are using several files and are making changes to these files then the different portions of file are saved on different locations on the disk. These chunks are linked and the operating system knows how to read the contents of file from the disk combining all the chunks. Similarly when we delete a file then the place where that file was stored on the disk is emptied and is available now to store other files. As the time goes on, we have a lot of empty and used pieces on the disk. In such situation we say that the disk is fragmented now. If we remove this fragmentation the chunks of data on the disk will be stored close to each other and thus reading of data will be faster. For the purpose of removing fragmentation on the disk the Defragmentation utility is used.

The compilers and interpreters also belong to the System Software category.

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What is programming

Definition: "A program is a precise sequence of steps to solve a particular problem.” It means that when we say that we have a program, it actually means that we know about a complete set activities to be performed in a particular order. The purpose of these activities is to solve a given problem. Alan Perlis, a professor at Yale University, says: "It goes against the grain of modern education to teach children to program. What fun is there in making plans, acquiring discipline in organizing thoughts, devoting attention to detail and learning to be self-critical? " It is a sarcastic statement about modern education, and it means that the modern education is not developing critical skills like planning, organizing and paying attention to detail. Practically, in our day to day lives we are constantly planning, organizing and paying attention to fine details (if we want our plans to succeed). And it is also fun to do these activities. For example, for a picnic trip we plan where to go, what to wear, what to take for lunch, organize travel details and have a good time while doing so. When we talk about computer programming then as Mr. Steve Summit puts it “At its most basic level, programming a computer simply means telling it what to do, and this vapid-sounding definition is not even a joke. There are no other truly fundamental aspects of computer programming; everything else we talk about will simply be the details of a particular, usually artificial, mechanism for telling a computer what to do. Sometimes these mechanisms are chosen because they have been found to be convenient for programmers (people) to use; other times they have been chosen because they're easy for the computer to understand. The first hard thing about programming is to learn, become comfortable with, and accept these artificial mechanisms, whether they make ``sense'' to you or not. “

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