Recap of C (Lecture 01)

Recap of C (Lecture 01)

Welcome to programming in C++. This will be 20 hour course, where we will
talk about various aspects of the C++ programming language and it will be divided naturally
into about 40 modules that you will study one after the other. The main emphasis of this course is to teach, how C++ programming language should be used in designing and implementing complex software
systems. So, you all will be aware that C++ is object
oriented or object based programming language and I would assume that you know C language, may not be at a very depth, but you have the overall idea about the C language. So, we will start from there, in the module
1, we will primarily talk about recapitulating various specific aspects of C programming. This is just to make sure that you can, if
required you can revisit those concepts and before we get deep into the C++ language,
you can be familiar with all the C programming requirements because C is a language, which is backward compatible to C++. So, we will first get started with recapitulation of C. So, these are objectives to revisit the concepts, particularly we will look into C Standard Library, besides the C language and programming aspects. We will briefly discuss about the organization of C program, how C program is to be organized possibly. So, far you have only written code in terms
of one single file using possibly 1 or 2 functions only. One of them must be main, as you know, we
will show how to organize programs better and with this we will have a foundation to;
for the C++ programming language. These are the different topics to be done,
the outline of the module; this is for reference. As the presentation, we will proceed on the
left of your screen, you will see this outline and it will be highlighted as to which particular
topic we are talking about. So, this is the first program “Hello World”
which I am sure all of you have studied. This is also the starting program in Kerning
and Ritchie’s famous book. We use ‘printf’ from the stdio library
and print the hello world on to the terminal or which is formally set to with the stdio
out file. The main function is one that you can see
here is where the execution starts and then you print this string and print backslash
n, which means you basically go to the next line; new line. C has a number of data types. Those are known as char, which is character;
int, float and double; float and double for the floating point numbers and integers are
for the so called whole numbers. Now, here I should mention that the C that
you commonly use is known as C89, C89 is a first standard of C that was created by ANSI,
the standardization organization and subsequently in 99, another standard was released, this
is called C99, so most of the compilers today follows C99 standard. We will also expect C99 to be followed. So, when we talk about C, we will try to highlight,
if few things have become different in C99. So, in terms of data type as you can see,
there is a new data type bool, which has got added in C99. In C89, you could still have Boolean values,
which can be true or false based on it being an integer value. So, if it is 0, it is false; otherwise it
is true. But in C99, there is a separate type bool. Every data type as you know, this built-in
data types has a size that is given in bytes and you can use size of operator to get that. You can define enumerated types which are
basically integer values which are given some symbolic names. Other data types in C include void. Void is not a type, it is very interesting
use and as we go into C++, we will see various different use of void. Void is where you would need to use a type,
you can use the type void, but it actually says that there is no type. So, it is like, when we do arithmetic we have
a 0. So, I can add 0 to x and it does not change
x. So, as we say every system needs a 0. So, void is a 0 of the type system, as we
will see more in C++. Then based on this built in types, there are
various derived types that supported the array, structure and union, pointer; we can have
functions and it is the commonly called, there is a string type in C called C strings these
days. Very strictly speaking string is not a type
in C, you will understand that more when we go into C++. C strings are actually a collection of functions
in string dot h header, which allow us to manipulate strings in C. Finally, the data
types can be modified for their size and whether they will be signed or unsigned and these
4 type modifiers are used in C. We will move on there are as you know the
variables in C. Variables have certain, their names can be defined in certain ways starting
with an alpha or an underscore and then extended with alpha numeric. Here are some examples of different variable
names, while it is often convenient to name variables with single letters or 1-2 letters. It is advised that you use variable names
which make some meaning. So, we are saying corrected end of session,
you could have just called it c or d or a, but it is better to give it in name from which
it can be understood as to what the variable means. When the variables are declared as they are
declared here, then the variables can be initialized also. That initialization is optional. So, when we say int i initialized with 10. It means that i is an int type variable whose
value at the point of definition itself will become 10. So, if you do not give initialization then
it is uninitialized variable which will have an unknown value to start with. Certainly, it is very good to initialize all
variables that we declare and define. C has a number of literals which are basically fixed values of built-in types depending on how you write a particular literal, the type
of that literal is decided. For example, if you just have a sequence of
numerals then it becomes a decimal integer type, but if you prefix that with 0, then
it is considered to be an octal type, a base eight number. If you prefix it with 0 x, then it is considered
to be a hexadecimal literal and so on. Character literals are within single quotes
and string literals are within double quotes. With C99, we have the introduction of what
is known as const types, that are constants and we will have more discussions of that
in depth when we do C++. So, in C89 the literals are basically fixed
values, but in C99, they are considered to be constant type data. So, 212 in C99 it will be considered a const
int. There are several operators in C; you will
be familiar with many of them. There are by common or binary operators like
addition, subtraction, multiplication. There are unary operations like negation. There are even ternary operations like question
mark, colon. Every operator has a fixed arity that is a
number of operands that it takes, which could be 1, 2 or 3. The operator in an expression is evaluated
according to their order of precedence. Some operators have higher precedence, some
have lower precedence. So, we know that if in the same expression
there is multiplication as well as addition; multiplication has to be done earlier wherever
it occurs in the expression. Similarly, if there are more than one of the
same operator in an expression then the order of their evaluation will depend on the associativity
and some operators are left to right, some operators are right to left. So, here I have shown the different examples. This is just for your reference, you will
certainly, if you know this. If you do not, please look up the text to
understand this well. Now, the next concept in C is an expression. That I have variables and I have operators. I have literals with those I can build expressions. So, expressions are defined in kind of a recursive
form will say that every literal is an expression. If I say number 5, it is an expression by
itself. Every variable is an expression and if I have
two expressions and connect them by a binary operator then that becomes a new expression. Similarly, I can have expressions with unary
operator, ternary operator and so on. Any function call that is done is an expression. So, the basic point is that expression must
have value; anything that has a value in C is called an expression. So, there are different examples you can see
here for the variables given here and different expressions are given below. Now, expressions cannot exist in C by themselves. So, expressions will have to exist as statement. A statement is a smallest unit of command
that you can specify in a C program. So, the simplest or the smallest statement
that you can have which is called a null statement is a semicolon itself. Otherwise, if you have an expression, you
can terminate that with a semicolon and once you terminate it with a semicolon then it
becomes a statement. So, if you look at the example below, in the
expression statement i plus j is an expression because i and j are variables and plus is
an operator connecting them, but the moment you write i plus j semicolon, it becomes a
statement. It can occur independently anywhere, similar
examples are shown for assignment for function call and so on. Besides the expression statement, C has a
number of control statements or control constructs, which basically allow the control flow in
the program to be managed. So, there are selection statements and loop
statements and so on. We will see little bit more of them in the
next slide and if there are number of statements one after the other which need to be grouped
for use, and then we put a pair of curly braces around them. We say it becomes a block and such a statement
is called a compound statement. So, that whole block of statements is a compound
one you can see an example at the bottom. Now, coming to control constructs which are
the key area of a C program which basically tell you, how the execution of the program
can happen. We have different ways to control, what will
be executed after one statement has been executed. By default we say, the C program has a fall
through control, which means that once a statement has been executed then the immediately next
statement in the program code will be the next statement to be executed, but we can
change that by the control flow. So, the first kind of control flow is a selection
statement; ‘if’ or ‘if else’. So, in the example as you can see that we
are saying, if a is less than b, then if that is true then you do the compound statement
that follows it. You can easily understand that what the compound
statement is saying that you interchange the value of a and b by using a third variable. If you look at the next example of if, it
is showing ‘if else’ kind of statement, where if x is less than 5 that if the condition
is true, it does one statement, else if the condition is false then it does another statement. You can see on that the false part has a compound
statement, whereas the true part as a single statement and selection can be done for a
multi way, in their multi way form that you can use the value of a variable. In this case we have used the variable i and
you can switch on that depending on what value the variable has taken, you take any one of
the cases that are listed. So, if i is one then case one will be selected
by which x will become 6 and we have a default case which is executed, if the value of i
does not fall among the different cases that exist. Statements like case as we have shown in switch
are also called labeled statement because there is a label to them. Then we have iteration statements where you
can repeat or loop statements very commonly these are called loop statements, where you
can have a ‘for’ loop which has three parts. An initial part I assigned 0, which is initially
done. A second condition part which is checked every
time the loop is executed and you continue in the loop provided that condition remains
true and there is a body which is basically what follows the ‘for’ statement, which
is the sequence of instructions or statements to be executed as a part of the loop and there
is a ‘end of loop’ statement like ++ i. Similarly, we have while loop we can have
do while iteration and the final type of control statements are ‘go to’, ‘continue’,
‘break’ and ‘return’. As you know, C advises that you should not
use ‘go to’. So, we are not showing example of ‘go to’,
if you design a C program well then you will not have any reason to use the ‘go to’
at all. So, try to only use ‘continue’ and ‘break’
along with loop and different switch statements to achieve your control flow, but you will
need ‘return’ to return from a function. So, these are the four types of different
types of control constructs that exist. To sum up what we have seen in this module
so far, we have seen what are the basic components of a C program, which is how do you do a IO,
how you; using the data type, how you define variables? How you initialize them? How to form them into expression using operators? How to convert the expressions into statements and different control flow statements to control the flow of the program? With this, we will end this part and next
we will talk about the derived types and how to use the derived types in C.

16 thoughts to “Recap of C (Lecture 01)”

  1. I just found these videos.But apparently this course isn't in the list of courses NPTEL is offering right now.
    So can't I take the online test anymore?

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