Functions
Sagor Chandro Bakchy
Assistant Professor
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Functions
Functions are block of code that can do any specific job
Once a function code is written it can be executed many
times
Basically two types of functions:
1. Built-in function/Library function
2. User Defined function
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Functions
Compiler provides pre-written functions called user defined
function
Example: printf(), scanf(), malloc(), calloc(), pow(), sqrt()
etc.
C allows to define functions according to user need. These
functions are known as user-defined functions.
Example: Suppose, you need to create a circle and color it
depending upon the radius and color. You can create two
functions to solve this problem:
createCircle() function
color() function
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Functions
Components of user defined function
1. Return type
2. Function name
3. Parameter list with type
4. Function body
5. Return statement
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Function’s Necessity
Functions help us in reducing code redundancy. If
functionality is performed at multiple places in software,
then rather than writing the same code, again and again, we
create a function and call it everywhere.
This also helps in maintenance as we have to change at one
place if we make future changes to the functionality.
Functions make code modular. Consider a big file having
many lines of code. It becomes really simple to read and use
the code if the code is divided into functions.
Functions provide abstraction. For example, we can use
library functions without worrying about their internal
working.
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Parameter Passing to functions
The parameters passed to function are called actual
parameters.
The parameters received by function are called formal
parameters.
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Parameter Passing to functions
There are two most popular ways to pass parameters.
Pass by Value/Call by Value: In this parameter passing
method, values of actual parameters are copied to function’s
formal parameters and the two types of parameters are stored
in different memory locations. So any changes made inside
functions are not reflected in actual parameters of caller.
Pass by Reference/Call by Reference: Both actual and formal
parameters refer to same locations, so any changes made
inside the function are actually reflected in actual parameters
of caller.
Parameters are always passed by value in C. If we need to
pass by reference it requires other coding.
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Parameter Passing to functions
1) Every C program has a function called main() that is called
by operating system when a user runs the program.
2) Every function has a return type. If a function doesn’t
return any value, then void is used as a return type. Moreover,
if the return type of the function is void, we still can use return
statement in the body of function definition by not specifying
any constant, variable, etc. with it, by only mentioning the
‘return;’ statement.
3) In C, functions can return any type except arrays and
functions. We can get around this limitation by returning
pointer to array or pointer to function.
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Parameter Passing to functions
4) Empty parameter list in C means that the parameter list is not
specified and function can be called with any parameters. In C, it is
not a good idea to declare a function like fun(). To declare a
function that can only be called without any parameter, we should
use “void fun(void)”.
**C++, an empty list means a function can only be called without
any parameter. In C++, both void fun() and void fun(void) are
same.
5)If in a C program, a function is called before its declaration then
the C compiler automatically assumes the declaration of that
function in the following way:
int function name();
And in that case, if the return type of that function is different than
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INT,
compiler would show an error.
Nested functions
Functions can be nested?
Answer is NO
But the following code works without error
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Nested functions
This not nested function rather it is scope of code
The view() function is accessible within fun() function
Coding like this some times creates anomaly in the output
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Example of Call by Value and Call by Reference
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Pass Array as argument:
void myFunction(int *param) { }
void myFunction(int param[10]) { }
void myFunction(int param[]) { }
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Pass Array as argument:
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Pass Multi Dimensional Array as argument:
Need to specify the dimension of array otherwise compiler will
consider the first [] as 1D array and generates error for the second
[]
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Recursive Function
A function that calls itself is known as a recursive function.
And, this technique is known as recursion.
Stops at a specific condition.
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Recursive Function
Factorial Finding
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Recursive Function
Factorial Finding
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Recursive Function
Summation of Natural numbers
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Recursive Function
Fibonacci Series
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Recursive Function
**Recursive function makes the code more aristocratic
What are the disadvantages of recursive programming over
iterative programming?
Note that both recursive and iterative programs have the same
problem-solving powers, i.e., every recursive program can be
written iteratively and vice versa is also true. The recursive
program has greater space requirements than iterative program
as all functions will remain in the stack until the base case is
reached. It also has greater time requirements because of
function calls and returns overhead.
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Pointers
What are pointers?
A pointer is a variable: its value is a memory address
like char variable has a character as a value and an int variable
has an integer as a value
whereas, the pointer variable has an address as a value
pointers are variables that contain memory addresses as their
values
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Pointers
The pointer in C language is a variable which stores the
address of another variable.
This variable can be of type int, char, array, function, or any
other pointer.
The size of the pointer depends on the architecture.
However, in 32-bit architecture the size of a pointer is 2
byte.
In my computer it is 4 bytes. (Not necessarily that 2byte for
32 bit so 8byte for 64 bit system)
It depends on internal architecture.
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Declaring a pointer
The pointer in c language can be declared using * (asterisk
symbol).
It is also known as indirection pointer used to dereference a
pointer.
int *a;//pointer to int
char *c;//pointer to char
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Advantage of pointer
Pointer reduces the code and improves the performance, it is
used to retrieving strings, trees, etc. and used with arrays,
structures, and functions.
We can return multiple values from a function using the
pointer.
It makes you able to access any memory location in the
computer's memory.
Thousands of pointer might point to one address that
reduces memory utilization.
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Usage of pointer
There are many applications of pointers in c language.
1) Dynamic memory allocation
In c language, we can dynamically allocate memory using
malloc() and calloc() functions where the pointer is used.
2) Arrays, Functions, and Structures
Pointers in c language are widely used in arrays, functions,
and structures. It reduces the code and improves the
performance.
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Example of pointer
In this code *p and *p2 indicates pointer declaration.
Only p indicates the value of the pointed address
*p shows the address of the pointer itself
Remember the syntax with * and without *
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Common mistakes when working with pointers
We want pointer pc to point to the address of c. Then,
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Common mistakes when working with pointers
But the following works. It is confusing. But true only at the
time of declaration.
Because
int *p = &c; is equivalent to
int *p:
p = &c;
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Pointers to array
We can pass the address of array into pointer. Look at the
following code and guess the output
We can use the pointers to use like array index accessing
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Some points about pointers
The unary operators * and ++ :
precedence: same
associate: from right to left
example:
total += *start++;
the pointer is incremented, not the value pointed to
The use of the postfix form (start++ rather than ++start)
means that the pointer is not incremented until after the
pointed-to value is added to total
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Some points about pointers
*p represents the value stored in a pointer.
++ is increment operator used in prefix and postfix
expressions.
* is dereference operator.
Precedence of prefix ++ and * is same and both are right to
left associative.
Precedence of postfix ++ is higher than both prefix ++ and *
and is left to right associative.
See the below example to understand the difference between
++*p, *p++ and *++p.
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Some points about pointers
arr[0] = 21, arr[1] = 30, *p = 21, q = 21
arr[0] = 21, arr[1] = 30, *p = 30, q = 21
arr[0] = 21, arr[1] = 30, *p = 40, q = 40
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Some points about pointers
*(ar + n): go to memory location ar, move over n units, and
retrieve the value there
Not get confused between *(dates+2) with *dates+2
*dates+2 means (*dates)+2:
*(dates+2); /* value of the 3rd element of dates */
*dates+2; /* 2 added to the value of the 1st element */
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Array passing as pointers
the four equivalent prototypes of a function sum() – with an
array as one of parameters
int sum(int *ar, int n);
int sum(int *, int);
int sum(int ar[], int n);
int sum(int [], int);
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Sorting: Bubble sort
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