C-Programming written by Santosh Or Kanchhi Chauhan

             C-Programming:- 

              Written by Santosh chauhan or Kanchhi chauhan

     ^{C-Programming-} 

          ^{Written by (Santosh chauhan Or kanchhi  chauhan)}

           

I have divided to this course in the 8 chapter.

Chapter 0 Introduction of C- Programming

Chapter 1 Variables, Constants and keywords.

Chapter 2 Instructions and operators

Chapter 3 Conditional statements

Chapter 4 Loop control statements

Chapter 5 Functions

Chapter 6 Recursion 

Chapter 7 Pointers

Chapter 8 Dynamic Memory Allocation

     

         ^{Chapter 0:-}

 

 ^{Computer Programming:->}

 ^{Computer programming is a medium for us to the communicate with computers, to communicate with each other}

 ^{programming is a way for us to deliver our instruction to the}

 ^computer.

    ^{C-Programming:->}

^{1.  C is a case sensitive programming language as well as}

 ^{one of the oldest programming language and finest}

 ^programming.

^{2.          C was developed by Dennis Ritchie AT and T’s Bell}

 ^{laboratory (USA) in 1972.}

^{Uses of C- Programming:-}

^{1.   All operating system (windows, Linux) are written in C-Programming.}

^{2.    C is used to driver programs for  device like Smart calculator, Printers as well as Tablets.}

^{3.  C is used to program  Embedded system where}

 ^{program need to run faster in limited}

 ^{memory(Microwave, Cameras).}

^{Chapter 1:->}

   Variables, Constants, and Keywords:

                   Variables:->

A variable is a container that stores a ‘values'. We have containers to storing Gram, sugar, etc. Similar to that variable in c stores the value of a constant.

 Example:

a = 4 a is assigned “4”

b = 3.7 b is assigned “3.7”

c = 'B' c is assigned “B”

Rules for naming variables in c:

1. The first character must be an alphabet or underscore(_).

2. No commas or blanks are allowed.

3. No special symbol other than underscore is allowed

4. Variable names are case sensitive.

                      Constants:->

An entity whose value doesn’t change is called a constant.

There are many types of constant:->

Primarily there are 3 types of constant:

1. Integer Constant 3,-6,8,9

2. Real Constant -342.1,5.5,9.0

3. Character Constant ‘a’,’$’,’@’(must be enclosed within single inverted commas)

                        Keywords:->

These are reserved words whose meaning is already known to the compiler. 

There are 32 keywords available in c:->

auto double int struct

break long else  switch

case return  enum typedef

char register extern union

const short float unsigned

continue signed for void

default sizeof goto volatile

do static if  while

   Our first C program:->

#include<stdio.h>

int main() {

printf(“Hello, C with Santosh is best cyber security channel");

return 0;

}

File :  first.c

The basic structure of a C program:->

All c programs have to follow a basic structure. A c program starts with the main function and executes instructions presents inside it. Each instruction terminated with a semicolon(;)

There are some basic rules which are applicable to all the c programs:->

1. Every program's execution starts from the main function.

2. All the statements are terminated with a semi-colon.

3. Instructions are case-sensitive.

4. Instructions are executed in the same order in which they are

 written.

       Comments:->

Comments are used to clarify something about the program in plain language. It is a way for us to add notes to our program. There are two types of comments in c:

Single line comment: //This is a comment.

Multi-line comment : /*This is multi-line comment*/

Comments in a C program are not executed and ignored.

Compilation and execution

A compiler is a computer program that converts a c program into machine language so that it can be easily understood by the computer.

A program is written in plain text. This plain text is a combination of instructions in a particular sequence. The compiler performs some basic checks and finally converts the program into an executable.

     Library functions:->

C language has a lot of valuable library functions which is used to carry out a certain task; for instance, printf function is used to print values on the screen.

printf(“This is %d”,i);

// %d for integers

// %f for real values

// %c for characters

      Types of Variable:-

Integer variables	int a=3;
Real variables	int a=7.7  (wrong as 7.7 is real) ;  float a=7.7;
Character variables	char a=’B’;

 

Receiving input from the user:-

In order to take input from the user and assign it to a variable, we use scanf function.

The syntax for using scanf:

scanf(“%d”,&i); // [This & is important]

& is the “address of” operator, and it means that the supplied value should be copied to the address which is indicated by variable i.

// %c for characters

           Chapter 2:-

Instructions and Operators:-

In the computer science, an instruction is single operation of a processor defined by the processor instruction set.

Types of instructions:

1.Type declaration instruction

2. Arithmetic instruction

3.Control instruction

Type of declaration instruction:

int a;
float b;

other variations:

int i = 10; int j = i, int a = 2;
int j1 = a + j - i;

float b = a+3; float a = 1.1;       ==>Error! As we are trying to use a before defining it. 

int a,b,c,d;

a=b=c=d=30;                         ==> Value of a,b,c & d will be 30 each. 

Airthmetic Instructions:-

Note:-

  1. No operator is assumed to be present

 int i=ab  ( Invalid )

    int i=a*b  ( valid )

2.There is no operator to perform exponentiation in c however we can use pow(x,y) from <math.h>(More later).

      Type Conversion:-

An Arithmetic operation between

int and int     ==> int
int and float   ==> float
float and float ==> float

5/2 --> 2               5.0/2 --> 2.5 //IMPORTANT!!
2/5 --> 0               2.0/5 --> 0.4 //IMPORTANT!!

NOTE:
int a = 3.5; //In this case, 3.5 (float) will be denoted to a 3 (int) because a cannot store floats.

float a = 8; // a will store 8.0 [8-->8.0(Promotion to float)]

  Operator Precedence in C:-

3*x-8y  is (3x)-(8y) or  3(x-8y)?

In the c language, simple mathematical rules like BODMAS no longer apply.

The answer to the above question is provided by operator precedence & associativity.

Operator precedence:-

The following table list the operator priority in C

Priority	Operators
1st	* / %
2nd	+   -
3rd	=

Operators of higher priority are evaluated first in the absence of parenthesis.

Operator associativity:-

When operators of equal priority are present in an expression, the tie is taken care of by associativity

 x  *  y  /  z =>  (x *  y) / z
x  /  y  *  z  =>  (x / y) * z

*, / follows left to right associativity.

Control instructions:-

Determines the flow of control in a program.

Four types of control instruction in C are:

1. Sequence Control Instruction

2. Decision Control Instruction

3. Loop Control Instruction

4. Case-Control Instruction

              Chapter 3: 

   Conditional  Statements

Conditional statements help you to make a decision based on certain conditions. These conditions are specified by a set of conditional statements having boolean expressions which are evaluated to a boolean value true or false.

Or

Conditional Statements in C programming are used to make decisions based on the conditions. Conditional statements execute sequentially when there is no condition around the statements. ... It is also called as branching as a program decides which statement to execute based on the result of the evaluated condition.

Decision-making instructions in C

If-else statement

Switch statement

If-else statement

The syntax of an if-else statement in c looks like this:

if ( condition to be checked) {

   Statements-if-condition-true ;

}

else{

statements-if-condition-false ;

}

Code Example

int a=23;

if (a>18){

printf(“you can drive\n”);

}

Note: -  that else block is not necessary but optional.

     Relational Operators in C

Relational operators are used to evaluate (true or false) inside the if statements. Some examples of relational operators are:

==	equals to
>=	greater than or equal to
>	greater than
<	less than
<=	less than or equal to
!=	not equal to

Important Note: 

'=' is used for an assignment, whereas '==' is used for an equality check.

The condition can be any valid expression. In C, a non-zero value is considered to be true.

        Logical Operators 

&&, ||, and ! are the three logical operators in C. These are read as “and,””or,” and “not.” They are used to provide logic to our c programs.

Use of logical operators:

1. && (AND) is true when both the conditions are true

    “1 and 0” is evaluated as false

    “0 and 0” is evaluated as false

    “1 and 1” is evaluated as true

2. || (OR) is true when at least one of the conditions is true. (1 or 0 = 1)(1 or 1 = 1)

3. ! returns true if given false and false if given true.

    !(3==3) evaluates to false

    !(3>30) evaluates to true

As the number of conditions increases, the level of indentation increases. This reduces readability. Logical operators come to the rescue in such cases.

Else if clause

Instead of using multiple if statements, we can also use else if along with if, thus forming an if-else if-else ladder.

if {

// statements ;

}

else if { //statements;

           }

else {  //statements;

        }

Using if-else if-else reduces indents. The last “else” is optional. Also, there can be any number of “else if.”

Last else is executed only if all conditions fail.

 

Operator Precedence

Priority	Operator
1st	!
2nd	*,/,%
3rd	+,-
4th	<>,<=,>=
5th	==,!=
6th	&&
7th	||
8th	=

 

Conditional operators

A shorthand “if-else” can be written using conditional or ternary operators.

Condition ?  expression-if-true ;  expression-if-false

Here, '?' and ':' are Ternary operators.

Switch case-control instruction

Switch-case is used when we have to make a choice between the number of alternatives for a given variable.

Syntax,

Switch(integer-expression)

{

Case c1:

       Code;

Case c2:                                                         //c1,c2,c3 are constants

       Code;                                                       //Code is any valid C code

Case c3:

      Code;

default:

      Code;

}

The value of integer-expression is matched against c1,c2,c3......if it matched any of these cases, that case along with all subsequent “case” and “default” statements are executed.

            Important notes:

• We can use switch case statements even by writing in any order of our choice
• Char values are allowed as they can be easily evaluated to an integer
• A switch can occur within another, but in practice, this is rarely done

      Chapter 4 - Loop Control                                                            Instruction

What is loop in the computer programming:-

When sometimes to any statement, set of instructions and numeric digit again and again - want to print in the computer programming then - uses to loop.

 for eg. Printing 1 to 100, first 100 even numbers, etc.

Hence loops make it easy for a programmer to tell the computer that a given set of instructions must be executed repeatedly.

Types of Loops: 

Primarily, there are three types of loop in c language:

1.While loop

2.do-while loop

3.for loop

We will look into this one by one.

While Loop

While(condition is true) {

// Code                                         // The block keeps executing as long as the condition is true

// Code

}

An example:

int i=0;
while (i<10){
printf(“The value of i is %d”,i); i++;
}

Note:-

If the condition never becomes false, the while loop keeps getting executed. Such a loop is known as an infinite loop.

Increment and decrement operators:-

i++  (i is increased by 1)

i--  (i is decreased by 1)

printf(“—i=%d”,--i);

This first decrements i and then prints it

printf(“i--=%d”,i--);

This first prints i and then decrements it

• +++ operators does not exists => Important
• += is compound assignment operator just like -=, *=, /= & %= =>Also important

Do-while loop:

The syntax of do-while loop looks like this:

do {

//code;

//code;

}while(condition)

Do-while loop works very similar to while loop

While -> checks the condition & then executes the code

Do-while -> executes the code & then checks the condition

**do-while loop = while loop which executes at least once

 

For Loop

The syntax of for loop looks like this:

for( initialize; test; increment or decrement)

{

//code;

//code;

}

Initialize -> setting a lop counter to an initial value

Test -> checking a condition

Increment -> updating the loop counter

An example:

for(i=0;i<4;i++)
{
printf(“%d”,i);
printf(“\n”);
}

Output:

0

1

2

3

Quick Quiz: Write a program to print first n natural numbers using for loop.

A case of Decrementing for loop

for(i=5; i; i--)

   printf(“%d\n”,i);

This for loop will keep on running until i becomes 0.

The loop runs in the following steps:

1. i is initialized to 5
2. The condition “i” (0 or none) is tested
3. The code is executed
4. i is decremented
5. Condition i is checked, and the code is executed if it's not 0.
6. & so on until i is non 0.

The Break Statement in C:-

The break statement is used to exit the loop irrespective of whether the condition is true or false. Whenever a “break” is encountered inside the loop, the controls are sent outside the loop.

Let us see with an example: 

for (i=0; i<1000; i++){
printf("%d\n",i);
if (i==5){
break;
}
}

Output: 0, 1, 2, 3, 4, 5 and not 0 to 100.

The continue statement in c:

The continue statement in c is used to immediately move to the next of the loop. The control is taken to the next iteration, thus skipping everything below continue inside the loop for that iteration.

Let us look at an example:

int  skip=7;
int i=0;
while(i<10){	
if(i  != skip)	
continue;
else
printf(%d”,i);
}

Output: 7 and not 0................9

Notes:

1. Sometimes, the name of the variable might not indicate the behavior of the program.

2. Break statement completely exits the loop

3. Continue statement skips the particular iteration of the loop

           Chapter 5 - Functions 

What is function?

Functions in C/C++......

Function is a group of statement which can perform the specific task in the Programming.

Or

A function is a set of statements that take inputs, do some specific computation and produces output.

Example and syntax of a function:

#include<stdio.h>
void  display();                   // Function prototype
int main(){
int a;
display();                          // Function call
return(0);
}

void display(){                           // Function definition
printf(“Hi I am display”);
}

Function prototype:

Function prototype is a way to tell the compiler about the function we are going to define in the program.

Here void indicates that the function returns nothing.

Function call:

Function call is a way to tell the compiler to execute the function body at the time the call is made.

Note that the program execution starts from the main function in the sequence the instructions are written.

Definition of Function Implementation: 

This part contains the exact set of instructions that are executed during the function call. When a function is called from main(), the main function falls asleep and gets temporarily suspended. During this time, the control goes to the function being called when the function body is done executing main() resumes.

 Important Points:

• Execution of a c program starts from main()
• A c program can have more than one function
• Every function gets called directly or indirectly from main()
• There are two types of functions in c. Let's talk about them.

Types of Functions:

• Library functions: Commonly required functions grouped together in a library file on disk.
• User-defined functions: These are the functions declared and defined by the user.

Why use functions?

• To avoid rewriting the same logic again and again
• To keep track of what we are doing in a program
• To test and check logic independently

Passing values to functions:

We can pass values to a function and can get a value in return from a function

int sum(int a, int b)

The above prototype means that sum is a function which takes values a(of type int) and b(of type int) and returns a value of type int

Function definition of sum can be:

int   sum(int a, int b){

int c;                                      => a and b are parameters

c=a+b;

return c;

}

Now we can call sum(2,3) [here 2 and 3 are arguments]; from main to get 5 in return.

int d=sum(2,3);   => d becomes 5

Note:

1. Parameters are the values or variable placeholders in the function definition. Ex: a & b

2. Arguments are the actual values passed to the function to make a call. Ex: 2 & 3

3. A function can return only one value at a time.

4. If the passed variable is changed inside the function, the function call doesn’t change the value in the calling function.

int change(int a){

a=77;                         => Misnomer

return 0;

}

change is a function which changes a to 77. No, if we call it from main like this.

int b=22;

change(b);                            => The value of b remains 22

printf(“b is %d”,b);                => prints “b is 22”

This happens because a copy of b is paused to the change function.

   Chapter 6:    Recursion

Recursion:

A function defined in C can call itself. This is called recursion.

A function calling itself is also called a recursive function.

Example of Recursion:

A very good example of recursion is factorial

factorial(n) = 1x 2 x 3...........x n

factorial(n)= 1 x 2 x 3...........n-1 x n

factorial(n)= factorial of (n-1) x n

Since we can write factorial of a number in terms of itself, we can program it using recursion.

// Function to calculate factorial using recursion

int factorial(int x){
int f;
if(x==0||x==1)
return 1;	
else
f=x * factorial(x-1);
return f;
}

How does it work?

Important Notes:

1. Recursion is sometimes the most direct way to code an algorithm

2. The condition which doesn’t call the function any further in a recursive function is called the base condition.

3. Sometimes, due to a mistake made by the programmer, a recursive function can keep running without returning, resulting in a memory error.

        Chapter 7 - Pointers

A pointer is a variable that stores the address of another variable.

i - 72,               j -87994

Address - 87994.           Address - 87998

j is a pointer

j points to i.

The "address of" (&) operator

The address of operator is used to obtain the address of a given variable

If you refer to the diagrams above

&i=> 87994

&j=>87998

Format specifier for printing pointer address is ‘%u’

The "value of address" operator (*)

The value at address or * operator is used to obtain the value present at a given memory address. It is denoted by *

*(&i) = 72

*(&j) = 87994

How to declare a pointer?

A pointer is declared using the following syntax,

int *j;  => declare a variable j of type int-pointer

j=&i     =>store address of i in j

Just like pointer type integer, we also have pointers to char, float, etc.

int *ch_ptr;       -> pointer to integer

char *ch_ptr;      -> pointer to character

float *ch_ptr      -> pointer to float

Although it's a good practice to use meaningful variable names, we should be very careful while reading & working on programs from fellow programmers.

A Program to demonstrate Pointers:

#include<stdio.h>

int main()

{

int i=8;

int *j;

j=&i;

printf(“Add i=%u\n”,&i);

printf(“Add i=%u\n”,j);

printf(“Add j=%u\n”,&j);

printf(“Value i=%d\n”,i);

printf(“Value i=%d\n”,*(&i));

printf(“Value i=%d\n”,*j);

return 0;

}

Output:

Add i=87994

Add i=87994

Add j=87998

Value i=8

Value i=8

Value i=8

This program sums it all. If you understand it, you have got the idea of pointers.

Pointers to a pointer:

Just like j is pointing to i or storing the address of i, we can have another variable, k which can store the address of j. What will be the type of k?

int **k;

k= &j;

i - 72,          j -87995,  k-86445

Address - 87994.  Address - 87998

Address

We can even go further one level and create a variable l of type int*** to store the address of k. We mostly use int* and int** sometimes in real-world programs.

Types of function calls

Based on the way we pass arguments to the function, function calls are of two types.

Call by value -> sending the values of arguments.

Call by reference -> sending the address of  arguments.

Call by value:

Here the values of the arguments are passed to the function. Consider this example:

int c = sum( 3 , 4 );   =>  Assume x=3 and y=4

If sum is defined as sum(int a, int b), the values 3 and 4 are copied to a and b. Now even if we change a and b, nothing happens to the variables x and y.

This is call by value.

In C, we usually make a call by value.

Call by reference:

Here the address of the variable is passed to the function as arguments.

Now since the addresses are passed to the function, the function can now modify the value of a variable in calling function using * and & operators. Example:

void swap(int *x, int *y)
{
int temp;
temp= *x;
*x = *y;
*y = temp;
}

This function is capable of swapping the values passed to it. If a=3 and b=4 before a call to swap(a,b), a=4 and b=3 after calling swap.

int main()
{
int a=3;	// a is 3 and b is 4
int b=4;
swap(a,b)
return 0;	// now a is 4 and b is 3
}

 

Chapter 8 - Dynamic Memory Allocation

Dynamic Memory Allocation:

Dynamic memory allocation is a way to allocate memory to a data structure during the runtime we can use DMA function available in C to allocate and free memory during runtime.

Function for DMA in C

Following functions are available in C to perform dynamic memory allocation:

1. malloc()
2. calloc()
3. free()
4. realloc()

malloc() function

Malloc stands for memory allocation. It takes number of bytes to be allocated as an input and returns a pointer of type void.

Syntax:

The expression returns a NULL pointer if the memory cannot be allocated.

calloc() function

calloc stands for continuous allocation.

It initializes each memory block with a default value of 0.

Syntax:

ptr = (float*) calloc(30*sizeof(int)) //Allocates Contiguous space in memory for 30 blocks

If the space is not sufficient, memory allocation fails and a NULL pointer is returned.

free() function

We can use free() function to allocate the memory.

The memory allocated using calloc/malloc is not deallocated automatically.

Syntax:

free(ptr);      => Memory of ptr is released

realloc() function

Sometimes the dynamically allocated memory is insufficient or more than required.

realloc is used to allocate memory of new size using the previous pointer and size.

Syntax:

ptr = realloc(ptr,newSize);
ptr = realloc(ptr, 3* sizeof(int)) //ptr now points to this new block of memory, which is capable of storing 3 integers