[Header]Classifying the FOR loop

mithunjacob · #1 20-Jun-2004, 16:39

Name/Brief Description:
Classifying the FOR loop explains the working of a header file with which it's possible to treat the FOR Loop as an object.

Date of Original Submission:
June 21st 2004

Submitted by:
Mithun Jacob a.k.a Phantom XXIII

License:
Open source

Detailed Description:
I'm sure many a programmer has been frustrated by the bulkiness and unwieldy nature of the nested FOR loop. When I was creating a solution to the N Queen Problem, I wished I could treat the FOR loop itself as an object, which could be dynamically created from a single class with specific constraints, and other useful techniques which are used in optimizing the brute-force modus operandi.

So, I created the following class keeping in mind the practical example of a
counter. The class basically creates a counter of customizable width, range,
and other knick-knacks like initial values, and whether it is continuous or
not. I have used INT as the data type...the class can be easily modified to
suit your needs.

Alright, enough with the introduction, here's the code:

CPP / C++ / C Code:

#include <iostream.h>
#include <conio.h>
#include <stdlib.h>

class dig
{
public:
int val;
int min;
int max;

dig( int mi=0, int ma=9)
{
val=mi,max=ma,min=mi;
}

int hitMax()
{
return (val==max);
}
};

This class represents each digit of the counter. As you can see,
val : holds the value of the digit or whatever unitary value
min : minimum value
max : maximum value
hitMax() : returns a flag stating whether
the max value is attained.

And the counter, itself, I'm presenting it in parts, the entire code is attached.

CPP / C++ / C Code:

class counter
{
dig *digs;

public:
int upd;
int digNo;
int beg;
int continuous;

/*digs                   : will hold the future digits of the counter, 
                             dynamically  allocated
 upd                    :  flag, will determine whether the counter should     
                             be updated or not
 digNO                 :  Total number of digits
 beg                    :  flag, determines whether this is the first run of 
                             the counter
 continuous          :  flag, will determine whether the counter must  
                             stop after finishing it's run or reset and start  
                             again*/

void init(int n,int c=0)
{
digNo=n;
digs=new dig[digNo];
continuous=c;
upd=1;
beg=1;
}

Pretty obvious..

CPP / C++ / C Code:

counter(){}

counter(int n, int c=0) {init(n,c);}

void set()
{
upd=1;
}

void reset()
{
for(int i=0;i<digNo;++i) digs[i].val=digs[i].min;
if(continuous) upd=1;
else upd=0;
}

Again, pretty obvious..

CPP / C++ / C Code:

int val(int no)
{
if(no>=0 && no<digNo) return digs[no].val;
else return -1;
}

void digSet(int no, int ma, int mi, int va)
{
digs[no].max=ma,digs[no].min=mi,digs[no].val=va;
}

~counter()
{
delete digs;
}

int val(int) : if the digit number is valid, the value is displayed.
I chose -1, as by default ALL my digits were in 0->9

void digSet(int, int , int , int): This function is used to change the
range or starting value of any digit.

And now, the backbone, of the class..

CPP / C++ / C Code:

int update()
{
if(upd)
{
	for(int i=digNo-1;i>=0;--i)
		{
		if(digs[i].hitMax())
			{
			if(i==0)
				{
				reset();
				break;
				}
			else digs[i].val=digs[i].min;
			}
		else
			{
			++digs[i].val;
			break;
			}
		}
if(beg==1)
	{
	for(int i=0;i<digNo;++i) digs[i].val=digs[i].min;
	beg=0;
	}
}
return upd;   }

This FOR loop scans through all the digits checking whether the maximum is attained in any one of them.

if(i==0)
{
reset();
break;
}

If a maximum is attained in the first digit, then the counter's run is over

[i]else digs[i].val=digs.min;

Else assign the minimum value to the digit.

And the flag 'upd' is TRUE if the counter is successfully updated.

There, it's a pretty simple piece of code, but I find it pretty useful.
Here's an application of the code:

CPP / C++ / C Code:

//Application of "counter.h"
#include <fstream.h>
#include <conio.h>
#include "counter.h"

void main()
{
counter number(2,1);

//Suppose you wanted all nos. less than 50, then all of //you have to do is
//number.digSet(0,4,0,0);

for(;;number.update())
{
        for(int i=0;i<2;++i) cout<<number.val(i);
                	
	    if(getch()==27) break;
 //27 is ASCII for the Escape key
                        clrscr();
}

}

Well, I suppose this wraps up the tutorial. I'll leave it's applications to your imagination...

A brief description of brute-forcing:
Brute-forcing is simply another, less desirable but effective solution to certain problems. For example, suppose you knew a password started and ended
with the string "CH" and consisted of six alphabets, obviously you'd try,
CHaaCH
CHabCH
CHacCH
.
.
.
CHbaCH
CHbbCH
CHbcCH
.
.
CHupCH
CHuqCH
CHurCH---------------->BINGO!

That's what brute-forcing is all about...trying out all the different
combinations, well..basically. Of course, there are different methods to brute-force. There is the dictionary option where you wil only compare words which make sense, not meaningless combinations like CHabCH..using a dictionary based brute-forcer you would have got the answer in no time.

Now, let me try to implement this in C++ using nested FOR loops, which are
basically FOR loops inside other FOR loops, inside other FOR loops..so on...

CPP / C++ / C Code:

for(char first='a';first<='z';++first)
	for(char secnd='a';secnd<='z';++secnd)
		cout<<"nCH"<<first<<secnd<<"CH";

Here, I'm assuming the required characters are in lower-case.

Mithun Jacob a.k.a Phantom XXIII
January 4th 2004
Contact:
mithunjacob@vit.ac.in / phantom@phantom23.tk / mithunjacob@hotmail.com
Site : http://www.phantom23.tk

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