QUIZ3

4 locations

LHC 502-505

LHC 401

CSC PCLABS 1,2,3,5,6

GCL - BHARTI BUILDING (4TH FLOOR)

TIME: 8 - 10PM

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PRINCIPLES OF GOOD PROGRAMMING

1. COMMENT YOUR CODE

2. INDENT CODE

3. USE MANY SMALL FUNCTIONS INSTEAD OF ONE LARGE FUNCTION

SCOPE
			num=3, y=5.6
ret_type (ex: char) func_name(int num, float y, int arr[])
{
	int c; float b;  [LOCAL VARIABLES]
	int q[5];
        b=10.5;
	arr[4]=7; ( nums[4] gets modified in main() )	
        arr[15]=8; (can get SEGMENTATION FAULT error)	
return 'f';  [function ends/exits at return]
	x=y+z;
}
SCOPE OF b,c in func_name is LOCAL to that function only

int main()
{ 
  int b=3; float c=5.6;
  char d; int q[6];
  int nums[10];
  d=func_name(b, c, nums);
 b=5;

}

PASSING OF PARAMETERS

1. PASSING BY VALUE: when variable is given as input, only the VALUE of variable is passed to the function

2. PASSING BY REFERENCE: when array is given as input, only the starting ADDRESS in memory of the array is passed to function

Q. CAN WE DEFINE FUNCTIONS AFTER MAIN?

DECLARATION:

char  func_name(int, float, int []);
 [not mentioned variable names, no body is given]

int main()
{ func_name.....
body
}

DEFINITION 

char func_name(int b, float c, int arr[])
{ body of function}

PASSING BY REFERENCE

MEMORY
ADD  VARIABLE STORED
14	--
15	--
16	--
17	nums[0]
18	nums[1]
19	nums[2]
20	nums[3]
21	nums[4]
.....
26	nums[9]

ON CALLING func_name

34   b   LOCAL VARIABLES OF func_name
35   c
36   arr  ---> 17 gets stored (address of nums[0])
37   q[0]
38   q[1]
39   q[2]
....

arr[4]  = 7
---

n C r =   n!/( (n-r)! * r!)

WRITE A C PROGRAM WHICH HAS FUNCTION  int ncr(int n, int r)
AND ANOTHER FUNCTION  int fact(int n)
MAIN FUNCTION TAKES USER INPUT FOR n,r AND PRINTS "n choose r"


RECURSION

1. n! =  n* (n-1)!

2. gcd(a, b) = gcd( b, a mod b)  [ assuming a>b]



int fact(int n)
{
	int result;
	if (n>0)
	     result=n*fact(n-1); [RECURSION, function calls itself]
	 else
		result=1;

	return result;
}

WHAT HAPPENS?

fact(3): result=3*fact(2)

fact(2): result=2*fact(1)

				|
		fact(1): result=1*fact(0)
						|
					fact(0):
						result=1;
					return result;					
					       |
		  fact(1): result=1*1;return result;
		  	   		     |
fact(2): result = 2*1; return result;