/prog/ - Programming

>>2068

That's fine. It's not for school, it's for fun/autism

I lost my first bit of source code, but I have some notes of it written own in one of my [paper] notebooks.

I'll post a copy of it when I'm done retyping it

#include <iostream>
using namespace std;

int n;
int m;
int a;
int b;
int c;
int d;
int e;
int f;

//functions//


int factorial1(int n) {
  int result = 1;
  for(int a = 1; a < n; a++) {
    result *= a;
  }
  return result;
}


int factorial2(int m) {
  int result = 1;
  for(int b = 1; b < m; b++) {
    result *= b;
  }
  return result;
}


int factorial3(int c) {
  int result = 1;
  for(int d = 1; d < c; d++) {
    result *= d;
  }
  return result;
}


int subtraction (int n, int m)
{
	int c;
	c = n - m;
	return c;
}

int multiplication (int b, int d)
{
	int e;	
	e = b * d;
	return e;
}

int division (int a, int e)
{
	int f;
	f = a / e;
	return f;
}


int main ()
{



cout << "Please enter the number of dimensions of the form in question.\nWe'll call this the n-value.\n";
cin >> n;
cout << "Now we can find the number of m-dimensional forms in an n-dimensional object.\nPlease define the m-value. Note that it should be equal to or less than the value of m.\n";
cin >> m;


a = factorial1 (n);
b = factorial2 (m);
c = subtraction  (n, m);
d = factorial3 (c);
e = multiplication (b, d);
f = division (a, e);



cout << f;


system ("PAUSE") ;
return 0;

}

Here's what I have so far. IDK why it doesn't work. For some reason the functions don't seem to be working, so there's no "f" to "cout <<"

10/10 would laugh again

>not using permutations to calculate combinations

uint permu(uint x, uint y) {

uint k = x-y;

uint j = x;

while(–j>k) x *= j;

return x;

}

uint comb(uint x, uint y){

return perm(x,y)/fact(y);

}

>>2303

Eh he's just learning

>>2302

There are a few problems here, namely:

1.) There is no reason to declare all of those variables at the beginning of the file

2.) There is no reason to declare all of those variables in the first place

3.) You should only have one factorial function

4.) The "subtraction", "multiplication", and "division" functions really shouldn't exist

5.) Using the system() function is almost always wrong - in this case, use cin.get() (or better yet, don't lock up the terminal at all)

This:

>https://clbin.com/ROf0S

Will reproduce the table in >>2189

I rearranged the original equation slightly, though.

Bonus points and cake if you can guess why. It wasn't to make it faster.

Using recursion:

int factorial(int a) {

if (a == 1) {

return 1;

}

int b = factorial(a-1);

return a*b;

}

>>2320

Thanks, I'll check it out when I get home. I've just been learning to program over the past few weeks so I'd say 97% of it is stuff I don't know

Oh, and one other question: why should I use std::cout instead of using namespace std?

>>2324

>Oh, and one other question: why should I use std::cout instead of using namespace std?

A "namespace" groups things together so that two objects sharing the same name don't conflict with eachother.

For example, if you created your own "cout", like this:

#include <iostream>
#include <fstream>

int main(void)
{
    // Please don't actually name your variable "cout"
    std::ofstream cout("some_file.txt");

    cout << "This gets saved to a file" << std::endl;
    std::cout << "This gets printed on the screen" << std::endl;

    return 0;
}

This works fine, since "cout" is in a different namespace than "std::cout".

If you were to use "using namespace std" though (and removed all the "std::" parts),

then "This gets printed on the screen" would also be written to the file, since the local

"cout" overloads the global one.

Of course, for simple programs, it doesn't actually matter - the "rule" is for complex programs with lots of namespaces.

tl;dr - Be specific so that the computer and other programmers know what the hell you're trying to do

>>2322

recursion is bad and has no place in real life applications. write iteratively.

>>2353

>has no place in real life applications

Yeah, totally. Who needs those shitty "parsers" anyway?

>>2363

Shift-reduce parsers are typically superior to recursive descent parsers. RD is just easier to implement by hand.

>>2433

>https://en.wikipedia.org/wiki/Moving_the_goalposts#Logical_fallacy

>>2032

What the fuck? You calculate n choose k by using pascal's triangle + memoization. Does anyone on /prog/ know how to program?

#include <stdio.h>
#include <stdint.h>
/* col > row is undefined */
uint64_t tb[5000][5000];
uint64_t pascal(const uint64_t row, const uint64_t col) {
	if(!col || col == row) return tb[row][col] = 1;
	if(tb[row][col]) return tb[row][col];
	return tb[row][col] = pascal(row - 1, col - 1) + pascal(row - 1, col);
}
int main() {
	uint64_t n, k;
	while(scanf("%lld%lld", &n, &k) == 2) {
		printf("%lld choose %lld = %lld\n", n, k, pascal(n, k));
	}
	return 0;
}