This document discusses functions in C programming. It defines different types of functions like standard library functions, user-defined functions and main function. It explains how functions can be defined in any order and called from any other function. It also provides tips about functions like a C program needs at least one main function, function names should be unique, more function calls means slower execution.

1. Menu Management
1. Odd / Even
2. Leap Year
3. Prime No.
0. Exit
Your Choice?
20
10

2. # include ”goto.c”
main( )
clrscr( ) ;
gotorc ( 10, 20 ) ; printf ( ”1. Odd / Even” ) ;
gotorc ( 11, 20 ) ; printf ( ”2. Leap year” ) ;
gotorc ( 12, 20 ) ; printf ( ”3. Prime number” ) ;
gotorc ( 13, 20 ) ; printf ( ”0. Exit” ) ;
gotorc ( 15, 20 ) ; printf ( ”Your choice?” ) ;
scanf ( ”%d”, &choice ) ;
..
..
}
int choice ;

3. main( )
{
int choice ;
/* display menu */
scanf ( ”%d”, &choice ) ;
switch ( choice )
{
case 1 :
/* odd / even logic */
break ;
case 2 :
/* leap year logic*/
break ;
case 3 :
/*prime number logic*/
break ;
default :
printf ( ”a” ) ;
}
}
case 0 :
break ;
n t a
Escape
Sequences
printf ( ”aaa” ) ;
Long
Beep

4. switch ( choice )
{
case 1 :
break ;
case 2 :
break ;
case 3 :
break ;
case 0 :
break ;
default :
printf ( ”a” ) ;
}
Block Commands
CH2PR3.C
Odd / even
logic
CH2PR4.C
Leap year
logic
Prime no.
logic
Ctrl KR
Ctrl KR
Ctrl KR
CH2PR5.C

5. Other Block Commands
Ctrl KB
Ctrl KK
Mark block
Ctrl KV Move block
Ctrl KC Copy block
Ctrl KW Write block to file
Ctrl KY Delete block
Ctrl KH Hide or unmark block

6. Readjustments Necessary
case 1:
main( )
{
…
…
}
break ;
Delete Delete
Shift declarations
Only Shifting
Won’t Do

7. No while, No Menu
#include ”goto.c”
main( )
{
while ( 1 )
{
/*display menu*/
scanf ( ”%d”, choice ) ;
switch( choice )
{
case 1 :
…
break ;
case 0 :
break ;
}
}
int choice ;
} exit( ) ;

8. Requirements of A Menu
Infinite loop
switch

9. Surprised?
main( )
{
float a = 0.7 ;
if ( a 0.7 )
printf ( ”A” ) ;
else
printf ( ”B” ) ;
}
A

10. Appearances Are
Misleading main( )
{
float a = 0.7 ;
printf ( ”%d%d”, sizeof ( a ), sizeof ( 0.7 ) );
}
365 0.7
Integer Double
4 8

11. Binary of A Float
float a = 5.375 ;
Binary of 5 Binary of .375
101 .011
Binary of 5.375
101.011
Normalised form
1.01011 * 22
.375 * 2 = 0.750 0
.750 * 2 = 1.500 1
.500 * 2 = 1.000 1

12. The Actual Storage
Mantissa
32
0 1000 0001 01011000000000000000000
Positive
2 + 127
. 01011
1 8 23
Sign
Bit Biased
Exponent

13. Difference In double
Mantissa
64
1 11 52
Bias value
is 1023
Sign
Bit
Biased
Exponent

14. Binary of 0.7
.7 * 2 = 1.4 1
.4 * 2 = 0.8 0
.8 * 2 = 1.6 1
.6 * 2 = 1.2 1
.2 * 2 = 0.4 0
.4 * 2 = 0.8 0
.8 * 2 = 1.6 1
.6 * 2 = 1.2 1
.2 * 2 = 0.4 0
.4 * 2 = 0.8 0
. . . . . .
. . . . . .

15. 32 - bit
Recurring binary
equivalent of
0.7
64 - bit
Recurring binary
equivalent of
0.7
float a = 0.7 ;
if ( a 0.7 )
printf ( ”A” ) ;
else
printf ( ”B” ) ;
A

16. Overriding Defaults
336655 336655LL
00..77 00..77ff
if ( a 0.7f )
printf ( ”A” ) ;
else
printf ( ”B” ) ;
B

17. Exact Binary
main( )
{
float a = 5.375 ;
if ( a 5.375 )
printf ( ”A” ) ;
else
printf ( ”B” ) ;
}
B

18. Functions
main( )
{
Output:
I am in main
printf ( ”n I am in main” ) ;
}
bombay( )
{
printf ( ”n I am in Bombay” ) ;
}
kanpur( )
{
printf ( ”n I am in Kanpur” ) ;
}
Output:
I am in main
Functions
main( )
printf( )
scanf( )
getch( )
exit( )
gotorc( )
clrscr( )
for( )
while( )
if( )
switch( )

19. Categories
Functions
Std. Library User-Defined
printf( )
scanf( )
exit( )
clrscr( )
kanpur( )
bombay( )
gotorc( )
main( )

20. Calling Functions
main( )
{
printf ( ”n I am in main” ) ;
bombay( )
{
printf ( ”n I am in Bombay” ) ;
}
kanpur( )
{
printf ( ”n I am in Kanpur” ) ;
}
Output :
I am in main
I am in Bombay
bombay( ) ; kanpur( ) ; I am in Kanpur
}
Function Call
Function Def.

21. Tips
A C program is nothing but a collection
of 1 or more functions
If C program contains 1 function its name
must be main( )
If C program contains more than 1 function
then one of them has to be main( )
Execution of any C program always begins
with main( )
Function names in a program must be unique

22. Order, Order !
bombay( )
{
printf ( ”n I am in Bombay” ) ;
}
main( )
{
printf ( ”I am in main” ) ;
bombay( ) ;
}
Tip: Functions Tip: Functions ccaann bbee ddeeffiinneedd iinn aannyy oorrddeerr

23. More Calls, More Bills
main( )
{
printf ( ”n I am in main” ) ;
bombay( ) ;
bombay( ) ;
}
bombay( )
{
printf ( ”n I am in Bombay” ) ;
}
Tip: Tip: MMoorree tthhee ccaallllss,, sslloowweerr tthhee eexxeeccuuttiioonn

24. Nobody is Nobody’s Boss
main( )
{
kanpur( )
{
Tip: Any function can call
any other function
printf ( ”n I am in Kanpur” ) ;
bombay( ) ;
}
printf ( ”n I am in main” ) ;
bombay( ) ; kanpur( ) ;
}
bombay( )
{
printf ( ”n I am in Bombay” ) ;
kanpur( ) ;
} Tip: Any function can call
any other function

25. Local v/s STD v/s ISD Calls
main( )
{
printf ( ”n I am in main” ) ;
main( ) ;
}
Local Call - Recursive Function
Process - Recursion

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