Key Features of C Programming and Basic Code Execution Guide

If you remember in our previous lesson that is Introduction to programming and Data Structures we had talked

about most important features of C programming Those were Portability and less lines of code.

Let's explore some more features of C programming. Have you ever wondered, why a company like Google for example has

separate departments for carrying out different tasks for the same job? Suppose, if the job is to develop a

software, then there might be a separate department for requirement analysis, a separate department for separate department for requirement analysis,

a separate department for designing phase, or may be a separate department for

testing phase etc. What do you thing is the need of making so many departments for the

development of a single software? Think about it. One day, I typed at Google search box

highly effective study habbits. And one of the results that poped up is this. Don't attempt to cram all

your studying into one session. Successful students typically space their work over shorter periods

of time and rarely try to cram all of their studying into one or two sessions. That is what I like to emphasize about.

These two examples have something in common. To be successful in some task

that we want to accomplish, the best idea could be to divide a task into smaller tasks and then work

on them separately. The similar idea is adopted by the inventor of the language.

He defined the language as procedural language. which simply means dividing your gigantic program into much smaller

programs called procedures or functions so that we can easily work with them. So, everything in C is nothing but set of

procedures or functions and this is the main feature of C language. This is the distinction between

High level language and low level language. Here, high or low simply points to the Degree of Abstraction.

Abstraction means hiding system level details. Therefore, high degree of abstraction means less efforts to the user

or you can say more user friendliness. As we won't have to worry about what is happening inside.

Example could be simple text editor. You are just typing out the text and when completed hit the save button,

without even worrying about how it is getting stored? , where it is getting stored? etc.

This is called higher level of abstraction. On the other hand, lower degree of abstraction means

more efforts to the user. In this case you have to know each and every internal details

about the computer. Example of high level programming languages are

COBOL, FORTRAN, C++, LIPS, Pascal, Prolog etc. And that of the low level languages

is Assembly language. There is one more level which is called middle level

which is neither high nor low. C language is called middle level language. because it does make programming

simpler for human beings. But then, on the other hand it also allows us to access system level features

such as Direct access to memory through pointers, Bit manipulation using bitwise operators,

Writing assembly code within C code. Because of these unique features of C, C became a popular language

or you can say a popular choice for developing both system level applications like kernels, device drivers,

operating systems etc. and various software applications like games, editors and other

graphic rich applications. These things are called system level features.

Now, C offers wide variety of built in functions, standard libraries and header files.

This makes programming a cake walk for programmers and that is obviously a great advantage.

OK friends, after a long conversation on the feature of C programming, that we had up till now

Let's come to an example to give you an idea about how a C code looks like. And we will also explore what does each

line mean that we write in the code. Let's try to make the session even more dynamic. I would recommend you to please

download Code Blocks IDE to execute code on your own. Because as I already told you,

programming and data structures becomes more interesting when you get your hands little dirty. Code Blocks is an integrated development environment

that helps you in creating C programs efficiently. You must follow the link in the description below to know more about how to install Code blocks

in your computer. Now we are going to execute a very basic C code in code blocks.

And I will explain you, what does each line depict in the program. In the first line, I had written

comment using double slash. Compiler usually ignores the comments. They are meant for the users

or you can say developers for their better understanding. As I have written on the top

that this program will print the output Neso Academy on to the console window.

Console window is just a black screen. And you will see in a moment. Next I have written #include <stdio.h>

Let's try to understand what does it mean. #include - this so called command written over here

is called as pre-processor directive. Now, the common question that pops up immediately is

what is pre-processor? Pre-processor job is to replace the textual content which is actually

followed by hash symbol ( # ) with the actual content. You had simply written #include <stdio.h> in your code.

But pre-processor actually replaces this line with the actual file stdio.h. Actually, before the compilation process

begins, pre-processor does its job by replacing those texts which are followed by hash symbol in the code.

As the name itself suggests pre-processor which means processing done prior to the actual compilation

Previously, what you have is the source code. The code that I had written is called as source code

which is now converted to an expended op code or you can say expended source code

because of the pre-processor we had replaced those statements which are followed by hash symbol

with the actual content of the files. This obviously increases the size of the actual content.

And therefore called Expanded source code. After that it sends the code, to the compiler

and compiler does its normal processing converting source code to machine code. Therefore #include<stdio.h>

simply requests the processors to include the file stdio.h. Now what does stdio.h mean?

Stdio.h is standard input output file, with .h extension. This file, with the .h extension

is called header file. Header files usually consists of prototypes or you can say declaration

of the function that we need. For example- stdio.h consists of declarations of functions like

printf and scanf. printf function is used to print the contents, whatever is there inside

its parenthesis and scanf is used to take user input at run time.

Including the header file is important. As you need to tell that which functions you are going to use in your program.

Next I had written a wired looking expression int main followed by curly brackets.

And inside them you have are some statements written. Before explaining you what does it really mean

let me give you a brief overview about what is function and a variable. Whatever code you write in C

always consists of these two important elements. C function consists of group of statements

that are intended to solve a particular problem On the other hand, variables are the

entities used to store values which are used during computation. In our example we have function named main

And the statements of the main are enclosed within these curly braces. Here the purpose of main function

is to print Neso Academy as output. Note down one thing. You may have several functions inside

your program but the entry point from where the actual computation begins is the main function.

Compiler actually look forward to this particular function and it is the starting point of your program.

Now the basic syntax of defining a function looks like this. You have a return type.

Then you have a name of a function. Then parameter_type name_of_parameter parameter_type name_of_parameter

enclosed within these brackets. These are called parameters list. And inside you can say

you have some set of statements which are followed by these curly braces. Here in our example

return type of this function main is int. int is a short name of integer. That means, your function

after completing all its statements will return an integer value. You can see that the last statement

that I have written here is, return 0 It indicates that if your statements complete execution successfully, then return integer 0

and exit from the function. Else if something else goes wrong, it will return some other integer

other than 0. I will explain you in detail about the functions in up coming lectures.

For now, this is enough to know. In function syntax, after return type

you have to specify the name of the function It can be any name of your choice. But in my opinion it is better to choose

a name which will give you a clear picture about what your function will actually do. Like if a function is meant for

performing addition, then the name add looks more sensible It improves readability. But there is no hard and fast rule.

You can choose any name of your choice. Main function is pre defined. OK. you cannot change that name.

Main is pre defined already. After the name of the function, you can see some lists of parameters which are

enclosed within the round brackets. These are called the inputs to your function.

In our example, main function doesn't have any parameters. It is mostly defined like that way.

But if you want, you can add parameters arcc and arcv whose values is been provided at run time

using command line arguments. You don't have to worry about it right now. we will talk about them in detail later.

Now, let's come to the main content over here. printf(" Neso academy"); and return 0;

What does it really mean? Here, we have a function called printf which has one parameter closed within quotes.

If you see carefully, I haven't put any curly brackets after this printf function. I simply put a semi colon over here.

The reason behind this is that this function is pre-defined somewhere in the C standard library

which is the library containing definitions of many functions like printf. The advantage of such a library is that

we won't have to write down the codes of functions again and again. Instead we simply call them

whenever needed. So we just have to call the function instead of defining it once again.

Note- In comparison with the definition of the function everything is as it is

when you are calling a function. But at the end of the closing bracket you have a semicolon.

And won't have curly brackets after that. Using printf function, you would be able to print the output Neso Academy

on the console window. OK. let's execute the code. You simply click on Build

and Run button over here for the execution of your code. If you are writing the code for the first time,

then you have to use this Build and Run Let's click on it. Here you can see the output.

Neso Academy is printed. Right? With the information process returned 0.

Which simply means your program completed successfully. Note- Here because we are first

time we are executing the code therefore Build and Run both are required.

Build actually asks the compiler to build the machine code for the source code we had written.

And Run simply runs the code and produce the output. Run button is available over here.

If you are executing for the second time, you simply has to use this run button. If you are not making any changes to the code

then clicking on the run button is sensible. If you make any changes, then you have to build it again

and Run. There is one more important point I would like to mention.

As we had learnt that we write #include <stdio.h> to include the standard input output header file.

And I told you this header file contains the prototypes or declarations of the functions like printf.

And I also told you that C standard library consists of the actual definition of the functions like printf.

Then one important question, I would like to address is Why do we require different files

one for storing the prototypes of the functions and other for storing the actual code? The reason behind that is the header files

stdio.h consists of only the declarations of the functions. That tells your compiler which functions

you are going to use in your program. And your pre- processors simply combines those declarations with the actual source code

and produce Expanded source code. On the other hand, C standard library consists of actual definitions of the functions.

Now, there is a program called linker which actually maps down the prototypes

mentioned by the pre- processor to the actual codes written in this standard library. It simply maps

and does not copy paste the content like pre- processor. This separate process of linking

makes the computation of program a little faster. Imagine if the pre- processor does the job of getting all the actual definitions

of the functions to the source code. How hectic the task would be and it also increases the size of the

the code exponentially. Because this time you are adding actual definitions and not the prototypes.

And thus compiler has to do a lot of work to compile the program. And therefore the speed of compilation falls down drastically.

Therefore maintaining header files and standard library separately is essential. OK friends, we end this session now

But before you leave, here is a quick exercise for you. Install the Code Blocks

and try to execute the code on your own that we had written.

Make these changes to the code and see what happens. Please make the changes one by one

and not all at the same time. To actually know what happens to the code and we will be able to see the errors clearly.

Comment out the #include<stdio.h> Second thing, remove the semicolon after printf. Remove int return type from main

Instead of 0 in return write any integer value you want. Replace 0 with some character.

Characters are usually written with single quotes Replace 0 with some character. Characters are usually written with single quotes For example you may write return 'a'.

Remove semicolon after return. The errors are shown in the window below. Over here as you can see.

Under this build messages tab. If there is any error it will be shown over here.

As you can see, build is finished o errors, 0 warnings and 0 minutes and 2 seconds Right?

So your code is completed successfully. Kindly see the message generated by the compiler and try to understand them on your own.

That's it. See you in the next lecture. Bye.