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1. Sigma institute of engineering
SUBJECT: COMPUTER PROGRAMMING
AND UTILIZATION
PREPARED BY : group c
 ENROLLMENT NO:- NAME OF STUDENT
1. 140500119041 KANADE MAHENDRA
2. 140500119052 MAKWANA BHAVESH
3. 140500119054 MEHUL JHALA
ASSIGNED BY ;
PROF.SURESH CHAUDHARY

2. Topic :
functions

3. CONTENTS:
 Function
 Function example
 Vedio on functions
 Benefits of function
 Math library functions function prototype
 Function arguments
 C++ variables
 Global variable
 External variables
 Other variables
 Recursion
 Recursion example

4. Functions
 A function is a self contained block of code
that performs a particular task.
 Any C program can be seen as a
collection/group of these functions.
 A functions takes some data as input, perform
some operation on that data and then return
a value.
 Any C program must contain at least one
function, which is main().
 There is no limit on the number of functions
that might be present in a C program.

5.  For ex.
main()
{
message();
printf(“I am in main”);
}
message()
{
printf(“I am in message”);
}

6. Video on function

7. Benefits of functions
Divide and conquer
Manageable program development
Software reusability
Use existing functions as building
blocks for new programs
Abstraction - hide internal details
(library functions)
Avoid code repetition

8. 5.3Math Library Functions
 Math library functions
 perform common mathematical calculations
 #include <math.h>
 Format for calling functions
 FunctionName( argument );
 If multiple arguments, use comma-separated list
 printf( "%.2f", sqrt( 900.0 ) );
 Calls function sqrt, which returns the square root of
its argument
 All math functions return data type double
 Arguments may be constants, variables, or
expressions

9. Method Description Example
ceil( x ) rounds x to the smallest integer
not less than x
ceil( 9.2 ) is 10.0
ceil( -9.8 ) is -9.0
cos( x ) trigonometric cosine of x
(x in radians)
cos( 0.0 ) is 1.0
exp( x ) exponential function ex exp( 1.0 ) is 2.71828
exp( 2.0 ) is 7.38906
fabs( x ) absolute value of x fabs( 5.1 ) is 5.1
fabs( 0.0 ) is 0.0
fabs( -8.76 ) is 8.76
floor( x ) rounds x to the largest integer
not greater than x
floor( 9.2 ) is 9.0
floor( -9.8 ) is -10.0
fmod( x, y ) remainder of x/y as a floating-
point number
fmod( 13.657, 2.333 ) is 1.992
log( x ) natural logarithm of x (base e) log( 2.718282 ) is 1.0
log( 7.389056 ) is 2.0
log10( x ) logarithm of x (base 10) log10( 10.0 ) is 1.0
log10( 100.0 ) is 2.0
pow( x, y ) x raised to power y (xy) pow( 2, 7 ) is 128
pow( 9, .5 ) is 3
sin( x ) trigonometric sine of x
(x in radians)
sin( 0.0 ) is 0
sqrt( x ) square root of x sqrt( 900.0 ) is 30.0
sqrt( 9.0 ) is 3.0
tan( x ) trigonometric tangent of x
(x in radians)
tan( 0.0 ) is 0
Fig. 3.2 Math library functions.
Math Library Functions Revisited

10. 5.2Program Modules in C Functions
 Modules in C
 Programs combine user-defined functions with library
functions
 C standard library has a wide variety of functions
 Function calls
 Invoking functions
 Provide function name and arguments (data)
 Function performs operations or manipulations
 Function returns results
 Function call analogy:
 Boss asks worker to complete task
 Worker gets information, does task, returns
result
 Information hiding: boss does not know details

11. Function Prototype
 All Identifiers in C must be declared before they are used. This is
true for functions as well as variables.
 For functions, the declarations needs to be done before the first
call of the function.
 A function declaration specifies the name, return type, and
arguments of a function. This is also called the function
prototype.
 To be a prototype, a function declaration must establish types for
the function’s arguments.
 Having the prototype available before the first use of the function
allows the compiler to check that the correct number and types of
arguments are used in the function call.

12.  The prototype has the same syntax as the
function definition, except that it is
terminated by a semicolon following the
closing parenthesis and therefore has no
body.
 Although, functions that return int values
do not require prototypes, prototypes are
recommended.

13. Function Definition
 General form of any function definition is:
return-type function-name(argument declarations)
{
declarations and statements
}
 Return-type refers to the data type of the value
being returned from the function. If the return
type is omitted, int is assumed.
 The values provided to a function for processing
are the arguments.
 The set of statements between the braces is
called as the function body.

14. Arguments – Call by Value
 In C, all functions are passed “by value” by default.
 This means that the called function is given the values of its
arguments in temporary variables rather than the originals.
 For ex. main()
{
int a=4,b=5;
sum(a,b);
printf(“Sum = %d”,a+b);
}
sum(int a,int b)
{
a++;
b++;
printf(“Sum = %d”,a+b);
}

15. Arguments – Call by Reference
 When necessary, it is possible to arrange a function which can modify a variable
in a calling routine.
 The caller must provide the address of the variable to be set (generally, a
pointer to a variable), and the called function must declare the parameter to be
a pointer and access the variable indirectly through it.
 For ex: main()
{
int a=4,b=5;
sum(&a,&b);
printf(“Sum = %d”,a+b);
}
sum(int *a,int *b)
{
(*a)++;
(*b)++;
printf(“Sum = %d”,(*a)+(*b));
}

16. C++ Variables
• A variable is a place in memory that has
– A name or identifier (e.g. income, taxes, etc.)
– A data type (e.g. int, double, char, etc.)
– A size (number of bytes)
– A scope (the part of the program code that can use it)
• Global variables – all functions can see it and using it
• Local variables – only the function that declare local variables
see and use these variables
– A life time (the duration of its existence)
• Global variables can live as long as the program is executed
• Local variables are lived only when the functions that define
these variables are executed
16

17. Local Variables
• Local variables are declared inside the function
body and exist as long as the function is running
and destroyed when the function exit
• You have to initialize the local variable before
using it
• If a function defines a local variable and there was
a global variable with the same name, the function
uses its local variable instead of using the global
variable
17

18. Example of Defining and Using Global
and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
18

19. Local vs Global Variables
#include<iostream.h>
int x,y; //Global Variables
int add2(int, int); //prototype
main()
{ int s;
x = 11;
y = 22;
cout << “global x=” << x << endl;
cout << “Global y=” << y << endl;
s = add2(x, y);
cout << x << “+” << y << “=“ << s;
cout<<endl;
cout<<“n---end of output---n”;
return 0;
}
int add2(int x1,int y1)
{ int x; //local variables
x=44;
cout << “nLocal x=” << x << endl;
return x1+y1;
}
global x=11
global y=22
Local x=44
11+22=33
---end of output---

20. External Variables
 See the below example:
main()
{
extern int a;
printf(“Value of a = %d”,a);
}
int a=5;
Output: Value of a = 5

21. Recursion
 Recursion defines a function in terms of itself.
 It is a programming technique in which a
function calls itself.
 A recursive function calls itself repeatedly,
with different argument values each time.
 Some argument values cause the recursive
method to return without calling itself. This is
the base case.
 Either omitting the base case or writing the
recursion step incorrectly will cause infinite
recursion (stack overflow error).

22.  Recursion to find the factorial of any number:
int factorial(int x)
{
if(x<=1)
return 1;
else
return(x*factorial(x-1));
}

23.  Example: factorials
 5! = 5 * 4 * 3 * 2 * 1
 Notice that
 5! = 5 * 4!
 4! = 4 * 3! ...
 Can compute factorials recursively
 Solve base case (1! = 0! = 1) then plug in
 2! = 2 * 1! = 2 * 1 = 2;
 3! = 3 * 2! = 3 * 2 = 6;

24. 5.14 Example Using
Recursion: The Fibonacci Series
 Fibonacci series: 0, 1, 1, 2, 3, 5, 8...
 Each number is the sum of the previous two
 Can be solved recursively:
 fib( n ) = fib( n - 1 ) + fib( n – 2 )
 Code for the fibaonacci function
long fibonacci( long n )
{
if (n == 0 || n == 1) // base case
return n;
else
return fibonacci( n - 1) +
fibonacci( n – 2 );
}

25. 5.14 Example Using
Recursion: The Fibonacci Series
Set of recursive calls to function fibonaccif( 3 )
f( 1 )f( 2 )
f( 1 ) f( 0 ) return 1
return 1 return 0
return +
+return

26. 1 /* Fig. 5.15: fig05_15.c
2 Recursive fibonacci function */
3 #include <stdio.h>
4
5 long fibonacci( long );
6
7 int main()
8 {
9 long result, number;
10
11 printf( "Enter an integer: " );
12 scanf( "%ld", &number );
13 result = fibonacci( number );
14 printf( "Fibonacci( %ld ) = %ldn", number, result );
15 return 0;
16 }
17
18 /* Recursive definition of function fibonacci */
19 long fibonacci( long n )
20 {
21 if ( n == 0 || n == 1 )
22 return n;
23 else
24 return fibonacci( n - 1 ) + fibonacci( n - 2 );
25 }

27. output:
Enter an integer: 0
Fibonacci(0) = 0
Enter an integer: 1
Fibonacci(1) = 1
 Program
Output
Enter an integer: 2
Fibonacci(2) = 1
Enter an integer: 3
Fibonacci(3) = 2
Enter an integer: 4
Fibonacci(4) = 3
Enter an integer: 5
Fibonacci(5) = 5
Enter an integer: 6
Fibonacci(6) = 8
Enter an integer: 10
Fibonacci(10) = 55
Enter an integer: 20
Fibonacci(20) = 6765
Enter an integer: 30
Fibonacci(30) = 832040
Enter an integer: 35
Fibonacci(35) = 9227465

28. Thank You..