Heres a fun challenge for you guys

[btripp]

On my first csci test dealing with recursion and some other stuff I got a recursive problem that was the following.

Write a recursive function that takes in a course name and an integer(# of parenthesies). Have the function output the results to the screen. Example:

parenthesize("CSCI", 3);
the output of the above would be (((CSCI)))

another example would be
parenthesize("Bobby", 5);
output: (((((Bobby)))))

ok that was the first recursive problem on our first exam.

On the Final exam we had another recursive problem which was to calculate the following.

1+ (1/3) - (1/5) + (1/7) ..... (1/2n -1) // the series alternates.

The function would take an integer and return a float as the answer



For the above problems I had to do them within an hour but there were also 4 other problems on the test. This class was the second one for c++ at my school. The first test covered recursion, pointers, linked lists,pointers inside of classes (copy constructor, destructor all that fun stuff).

All of our tests are handwritten in 1 hour 15 mins to write programs. THere were absolutely no code correction problems , what is a string any of that stuff.

I would like to see what some of you guys come up with for these two above problems. I had to do them on the test in about 10-15 mins roughly. Just trying to give some of you guys a challenge. Have fun with it guys.

[helios]

template <typename T>
std::string parenthesize(const T &s,unsigned n){
	return std::string(n,'(')+s+std::string(n,')');
}

float f(unsigned n){
	float r=0;
	for (unsigned a=0;a<n;a++)
		r+=1.0f/(2.0f*a+1.0f);
	return r;
}

What kind of asshole would do this using recursion?

[btripp]

My teacher lol. I think he prides himself on making problems like that. Pretty much useless problems. I made an A in both of the programming classes but one of few. I think he tries to weed people out with problems like that. He succeeds too. We had 20 kids in the class at the beginning and ended up with 7 that passed.

heres how i did my parenthesize on the test

void parenthesize(string name, int num)
{
if(num < 1)
      cout << name << endl;
else
{
name = '(' + name + ')';
return parenthesize(name, num - 1);
{
}

[blackcoder41]

wow! i'm hearin' echo from hello, LOL :)

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#include <iostream> using namespace std; void parenthesize(string str, int par) { if(par<1) return; string s = '(' + str + ')'; cout << s << '\n'; parenthesize(s, --par); } int main(int argc, char* argv[]) { parenthesize("hello", 5); return 0; }

(hello) ((hello)) (((hello))) ((((hello)))) (((((hello)))))

[helios]

btripp:
Error:8: void value not ignored as it ought to be.
Error:8: void function returning value.

[btripp]

lol palm to face. its because i put return before parenthesize. when it doesnt return my b

[jRaskell]

My teacher lol. I think he prides himself on making problems like that. Pretty much useless problems. I made an A in both of the programming classes but one of few. I think he tries to weed people out with problems like that. He succeeds too. We had 20 kids in the class at the beginning and ended up with 7 that passed.

Sadly, there are many teachers like that, and frankly it's a downright pathetic attitude for a teacher to have.

[blackcoder41]

my teacher is an asshole!

[Bv202]

Well, as a beginner in C++, I perfectly understand Blackcoder's and brtipp's code, but do not understand the code of Helios.

So is using recursion that bad? Why?

EDIT:
Nvm, Helios' code is actually very easy lol..

[helios]

It's not bad. The problem is that recursive solutions are always more expensive than iterative ones. For one, because in languages like C and C++, the stack is limited. That imposes a practical limit on the input before the program fails, and recursive algorithms don't fail nicely, either.
Whenever possible, an iterative algorithm should be chosen over a recursive algorithm.

[S6k9GNh0]

template <typename T>
std::string parenthesize(const T &s,unsigned n){
	return std::string(n,'(')     //Create string with n number of parenthesis
                           +s               //Append original string.
                           +std::string(n,')'); //Append n number of parenthesis on the right side.
                           //And then return the finished string via return function.
}

This should help those who didn't understand helios's code at first.

helios, why make this a template function?

EDIT: The reason I ask is since the only thing that can append like this is a string, I'm confused as to why we need to ask the person using the function for what is most likely going to be an std::string.

I'd love to take test like this. I'm sick of being asked baby questions like what's an integer. I also laugh when I write a 2 page essay on it because I'm bored.

[helios]

helios, why make this a template function?

So that if the user passes a string literal or a char array, an extra std::string isn't unnecessarily constructed. Although right now I'm wondering if it would make the call ambiguous. I'd have to try it.

[Bv202]

I'm sick of being asked baby questions like what's an integer.

Good to know I'm not the only one in this situation.

[jLNv0pDG]

int main(int argc, char* argv[]) {

@blackcoder41: Why are there parameters in main?

[moorecm]

I guess I'll try doing the other one--in one line, of course! ;)

float f( unsigned int n )
{
    return ( n == 1 )? 1 : ( ( ( n % 2 )? -1 : 1 ) * ( 1.0 / ( 1 + ( ( n - 1 ) * 2 ) ) ) ) + f( n - 1 );
}

[jLNv0pDG]

"series"? --is that a variable / function?

[moorecm]

"series"? --is that a variable / function?

Oops! I renamed the function from "series" to "f" when I posted it and forgot to change the name in both places.

[blackcoder41]

farcear wrote:

Why are there parameters in main?

so that you could pass arguments to it, for example if you ever play counter-strike, it passes arguments notify half life to directly jump to counter-strike mode... the same with warcraft 3, it passes -windows for it to start in window mode. here's a sample code..

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#include <iostream> using namespace std; int main(int argc, char* argv[]) { if(argc>1) { cout << "you've pass \"" << argv[1] << "\" as an argument\n"; cout << "do something about the arguments.\n"; cout << "special execution or whatever..\n"; } else { cout << "execute normally\n"; } return 0; }

run this in commad prompt: >program.exe [output] execute normally >program.exe hello [output] you've pass "hello" as an argument do something about the arguments special execution or whatever.. note: don't type the > symbol

[blackcoder41]

Bv202 wrote:

Well, as a beginner in C++, I perfectly understand Blackcoder's and brtipp's code, but do not understand the code of Helios.

i'm glad, you've figured out helios code

[jLNv0pDG]

so that you could pass arguments to it

Is it not illegal/impossible/undesirable to call main()?

http://www.cplusplus.com/forum/beginner/17885/