Who invented C Language?

Dennis Ritchie in 1972 developed a new language by inheriting the features of both
BCPL and B and adding additional features. He named the language as just C.
Who invented B Language?
Ken Thomson at AT&T Bell Labs developed a language and named it B. Even the B
language was found to have some short comings to support development of both
business applications and system software.
Who invented BCPL Language?
Basic Combined Programming Language(BCPL) was developed by Martin Richards,
Cambridge university.
Why C Language?
C is one of the high level languages. It is a general purpose language, which means
it can be used to write programs of any sort.

C language is considered as the mother language of all the modern languages because most of
the compilers, JVMs, Kernals etc. are written in C language and most of languages follows c
syntax e.g. C++, Java etc.
It provides the core concepts like array, functions, file handling etc. that is being used in many
languages like C++, java, C# etc.
A system programming language is used to create system softwares. C language is
a system programming language because it can be used to do low level
programming (e.g. driver and kernel).

A procedural language breaks the program into functions, data structures etc.
C is a procedural language. In C, variables and function prototypes must be declared before
being used.
A procedural language specifies a series of steps or procedures for the
program to solve the problem.
What are the features of C Langauges?
What is a function?
A function is a set of statements to perform a specific task.
A function is a group of statements that together perform a task. Every C program
has at least one function, which is main()

You can divide up your code into separate functions. How you divide up your code among
different functions is up to you, but logically the division is such that each function performs a
specific task.
A function declaration tells the compiler about a function's name, return type, and parameters. A
function definition provides the actual body of the function.
The C standard library provides numerous built-in functions that your program can
call. For example, strcat() to concatenate two strings, memcpy() to copy one
memory location to another location, and many more functions.
A function can also be referred as a method or a sub-routine or a procedure, etc.

Defining a Function
The general form of a function definition in C programming language is as follows
return_type function_name( parameter list ) {
body of the function
}

A function definition in C programming consists of a function header and a function body. Here
are all the parts of a function

Return Type A function may return a value. The return_type is the data type of the
value the function returns. Some functions perform the desired operations without
returning a value. In this case, the return_type is the keyword void.

Function Name This is the actual name of the function. The function name and the
parameter list together constitute the function signature.

Parameters A parameter is like a placeholder. When a function is invoked, you pass a

Function Body The function body contains a collection of statements that define what
the function does.

Example
Given below is the source code for a function called max(). This function takes two parameters
num1 and num2 and returns the maximum value between the two
/* function returning the max between two numbers */
int max(int num1, int num2) {
/* local variable declaration */
int result;

if (num1 > num2)

Function Declarations
A function declaration tells the compiler about a function name and how to call the function.
The actual body of the function can be defined separately.
A function declaration has the following parts
return_type function_name( parameter list );

For the above defined function max(), the function declaration is as follows
int max(int num1, int num2);

Parameter names are not important in function declaration only their type is required, so the
following is also a valid declaration
int max(int, int);

Function declaration is required when you define a function in one source file and you call that
function in another file. In such case, you should declare the function at the top of the file calling
the function.

Calling a Function
To call a function, you simply need to pass the required parameters along with the function
name, and if the function returns a value, then you can store the returned value. For example
#include <stdio.h>
/* function declaration */
int max(int num1, int num2);
int main () {
/* local variable definition */
int a = 100;
int b = 200;
int ret;
/* calling a function to get max value */
ret = max(a, b);
printf( "Max value is : %d\n", ret );
return 0;
}
/* function returning the max between two numbers */
int max(int num1, int num2) {

/* local variable declaration */

We have kept max() along with main() and compiled the source code. While running the final
executable, it would produce the following result
Max value is : 200

Function Arguments
If a function is to use arguments, it must declare variables that accept the values of the
arguments. These variables are called the formal parameters of the function.
Formal parameters behave like other local variables inside the function and are created upon
entry into the function and destroyed upon exit.
While calling a function, there are two ways in which arguments can be passed to a function
S.
N.

Call Type & Description

This method copies the actual value of an argument into the formal parameter of the
function. In this case, changes made to the parameter inside the function have no effect on
the argument.
Call by reference

This method copies the address of an argument into the formal parameter. Inside the
function, the address is used to access the actual argument used in the call. This means that
changes made to the parameter affect the argument.

By default, C uses call by value to pass arguments. In general, it means the code
within a function cannot alter the arguments used to call the function.

The call by value method of passing arguments to a function copies the actual value of an
argument into the formal parameter of the function. In this case, changes made to the parameter
inside the function have no effect on the argument.

By default, C programming uses call by value to pass arguments. In general, it means the code
within a function cannot alter the arguments used to call the function. Consider the function
swap() definition as follows.
/* function definition to swap the values */
void swap(int x, int y) {
int temp;
temp = x; /* save the value of x */
x = y;
/* put y into x */
y = temp; /* put temp into y */
}

return;

Now, let us call the function swap() by passing actual values as in the following example
#include <stdio.h>
/* function declaration */
void swap(int x, int y);
int main () {
/* local variable definition */
int a = 100;
int b = 200;
printf("Before swap, value of a : %d\n", a );
printf("Before swap, value of b : %d\n", b );
/* calling a function to swap the values */
swap(a, b);
printf("After swap, value of a : %d\n", a );
printf("After swap, value of b : %d\n", b );
}

return 0;

Let us put the above code in a single C file, compile and execute it, it will produce the following
result
Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200

It shows that there are no changes in the values, though they had been changed inside the
function.

The call by reference method of passing arguments to a function copies the address of an
argument into the formal parameter. Inside the function, the address is used to access the actual
argument used in the call. It means the changes made to the parameter affect the passed
argument.
To pass a value by reference, argument pointers are passed to the functions just like any other
value. So accordingly you need to declare the function parameters as pointer types as in the
following function swap(), which exchanges the values of the two integer variables pointed to,
by their arguments.
/* function definition to swap the values */
void swap(int *x, int *y) {
int temp;
temp = *x;
*x = *y;
*y = temp;

/* save the value at address x */

return;
}

Let us now call the function swap() by passing values by reference as in the following example
#include <stdio.h>
/* function declaration */
void swap(int *x, int *y);
int main () {
/* local variable definition */
int a = 100;
int b = 200;
printf("Before swap, value of a : %d\n", a );
printf("Before swap, value of b : %d\n", b );
/* calling a function to swap the values.
* &a indicates pointer to a ie. address of variable a and
* &b indicates pointer to b ie. address of variable b.
*/
swap(&a, &b);
printf("After swap, value of a : %d\n", a );
printf("After swap, value of b : %d\n", b );
}

return 0;

Let us put the above code in a single C file, compile and execute it, to produce the following
result

Before swap, value of a :100

It shows that the change has reflected outside the function as well, unlike call by value where the
changes do not reflect outside the function.