Question

I keep getting error on this code, i know it's the comb(k-1,r) giving me the error, but i don't know why.
The code is suppose to generate next_Combination.

Answer 1

#include <iostream>
#include <algorithm>
using namespace std;

int arr[10]={0,1,2,3,4,5,6,7,8,9};
void switc(int a, int b){
int temp = arr[a];
arr[a]=arr[b];
arr[b]=temp;

return;
}

void print(int size){
for (int i=0;i<size;i++)
cout << arr[i] << " ";
cout << endl;
return;
}
long Factorial(long val)
{
long Result = 1;
for(long i = 1; i <= val; i++)
{
Result *= i;
}
return Result;
}
long Combination(long N, long R)
{
return (Factorial(N)) / ((Factorial(N-R)) * Factorial(R));
}

void comb(int n, int r){
int i;
int k= Combination(n, r);
if (k==0)
print(r);
else{
for (i=k-1;i>=0;i--){
switc(i,k-1);
comb(k-1,r);
switc(i,k-1);
}
}
return;
}

int main(){
while (1){
int n, n1;
cout<<"Enter a number: ";
cin>>n>>n1;

comb(n, n1);

cout<<"The Factoral for the combination is "<<Combination(n,n1)<<endl;
return 0;

}}

Answer 2

@e.mccormick

Answer 3

So the problem is in the recursion?

Answer 4

long Combination(long N, long R) { return (Factorial(N)) / ((Factorial(N-R)) * Factorial(R)); }

That is returning a long and you are passing it to a function that takes an int.

Answer 5

would it make a difference if i change long in to int?

Answer 6

Might. At that point it would be called properly. But you have to watch your casting.

Answer 7

Since they are the same on most systems, you might be able to just use ints all the way through.

Answer 8

i changed it, but it didn't make a difference, it still gives me an error

Answer 9

Or longs.

Answer 10

What exact error is it giving?

Answer 11

it wouldn't load the compiler.. it stops it before compiling and says that the program has stopped working

Answer 12

So it is some sort of logic error? Hmm... At that point, you may need to toss in some print statements or break points and find what things are doing right before the program breaks and see what values are being passed around. Also, how deep is your recursion going? How many calls?

Answer 13

If you have some insane depth you could hit a limit.
http://stackoverflow.com/questions/2630054/does-c-limit-recursion-depth

But that would be really deep to hit that unless something is causing it to chew up a ton of ram.

Answer 14

idk how deep the recursion is, it does factorial, so it could get a little deep wen im calling it several times with in a loop

Answer 15

What is sample input and output?

Answer 16

the input number i used were 5 and 3, but it wouldn't compile it, but it stops it

Answer 17

Yah, with those it should not get too deep. Hmm....

Answer 18

it doesn't compile? or it doesn't run?

Answer 19

it runs it up to Enter a number, then when i input two numbers, the program stops working

Answer 20

what is the code supposed to do?

Answer 21

permutation, combination, and arrangement.. the above code is suppose to be for combination..

Answer 22

```
if (k==0)
print(r);
else{
for (i=k-1;i>=0;i--){
switc(i,k-1);
comb(k-1,r);
switc(i,k-1);
}
}
```
What is this supposed to do?

Answer 23

it is suppose to calculate and print out the next_combination
ex. 012 013 032 312 etc.. it amount of numbers depends on what the user inputs

Answer 24

```
120 / 12
362880 / 4320
0 / 0
```

Answer 25

It's wrong, that part of it.

Answer 26

Hmmm.... yah... how large is that value getting! I wonder if it is exceeding 2147483647

Answer 27

Why are you swapping around the array anyway, that?

Answer 28

What should 5 3 as input provide?

Answer 29

so the numbers would have different arrangements,

Answer 30

5 & 3 is suppose to have 10 combination, each combination with 3 numbers like 123 231 312 etc

Answer 31

What exactly are you doing though? Are you just doing permutations?

Answer 32

i did the permutation already, and the permutation only requires one number since the formula is n! , but for the combination it is slightly different, it uses n!/r!(n!-r!), that's why it's getting a bit complicated for me

Answer 33

this is the original question if it helps
Write a C++ program to generate the followings: - Next/Previous permutation of n objects and calculate the total number of permutations of n objects. - Generate all the permutations of n digits. - Generate and calculate the number of combinations of n k by k digits. - Generate and calculate the number of arrangements of n k by k digits

Answer 34

what is nest/prev permutation mean?

Answer 35

something like this
Enter a number: 3
0 1 2
1 0 2
0 2 1
2 0 1
2 1 0
1 2 0
Press any key to continue . . .
The numbers that are generated are the next/prev permutation for 3

Answer 36

Okay, so why are you even counting combinations then?

Answer 37

Why aren't you printing the array?

Answer 38

the combination works similarly as the permutation and i use the recursion to calculate the combination, it worked for the calculation, but when i try to print the next/prev combination with the same method i used for permutation, it didn't work

Answer 39

You're not printing out an array.

Answer 40

You're only printing out the number of combinations

Answer 41

i thought it would print the combination too since it was able to do for the permutation. any suggestion what i should do

Answer 42

First have it print out the actual array

Answer 43

btw, this is the method i used for permutation, and it worked fine, but wen it comes to comb, not so much
<code>
void perm(int k,int size){
int i;
if (k==0)
print(size);
else{
for (i=k-1;i>=0;i--){
switc(i,k-1);
perm(k-1,size);
switc(i,k-1);
}
}
return;
}
<code/>

Answer 44

okay can you give me sample output then, for combinations?

Answer 45

Enter a number: 5 2
Press any key to continue . . .

Answer 46

now when i put numbers less than 5 it works for example
Enter a number: 4 3
0 1 2
0 1 3
0 3 2
3 1 2
The Factorial for the combination is 4
Press any key to continue . . .

Answer 47

so does it have to do with the limit of the recursion.

Answer 48

It would have to get insanely deep to do that, and I don’t think this is. But what about putting a few couts in there. Find out each step of the way what it is calling and returning. Use a pause so it only loops or recurses when you press a key. Then you can watch the values to see if they are doing something you did not expect.

Answer 49

Thanks guys, i'll come back to it tomorrow

Answer 50

The problem is you end up with 0/0

Answer 51

it isn't recursion

Answer 52

LOL! You even posted that before and I missed it. Was a bit distracted.... yah, 0/0 is a big deal in computers.

Answer 53

you did put that earlier, i didn't notice it.

Answer 54

so i need to have something like this ?

long Combination(long N, long R)
{
if (((Factorial(N-R)) * Factorial(R)) != 0)
return (Factorial(N)) / ((Factorial(N-R)) * Factorial(R));
else{
cout<<"Error! can't divide by zero. ";
}
}