The Big Programming Thread - Page 170

On September 26 2012 08:20 RoyGBiv_13 wrote:


Can vouch for that C/assembly/occasional machine code is way fun. Learning the complexity of the C language will unveil the mysteries of hardware. Also, <3 money.

Also, +1 for supporting python as a first language. Awesome scripting language that will generate a ton of ideas for programs right out the gate. Starting with languages like java or C, you have to know quite a bit about packages and design in order to do some of the simplest things like read file metadata to make a decision. Starting with a web language is great, but only if that is what you want to do, and its very much a one way street (harder to go down the stack than up).

On September 30 2012 10:16 lolmlg wrote:
To solve that problem properly you should really use an entirely different sort of solution. Google the phrase "dynamic programming". You should try to come up with a recursive algorithm that reduces the problem to a base case and then constantly checks partial solutions to determine what the best answer is.

On September 30 2012 10:04 white_horse wrote:
Ok I did that, but a little differently, thanks. But the change doesn't appear for the coins (dimes, nickels, pennies) when I run it. Here is the rest of the code:

numTenDollar = static_cast<int>(total)*100 / (10*100);
total = total - (numTenDollar*10);
numFiveDollar = static_cast<int>(total)*100 / (5*100);
total = total - (numFiveDollar*5);
numOneDollar = static_cast<int>(total)*100 / (1*100);
total = total - (numOneDollar*1);
numQuarter = static_cast<float>(total)*100 / (0.25*100);
total = total - (numQuarter*0.25);
numDime = static_cast<float>(total)*100 / (0.10*100);
total = total - (numDime*0.10);
numNickel = static_cast<float>(total)*100 / (0.05*100);
total = total - (numNickel*0.05);
numPenny = static_cast<float>(total)*100 / (0.01*100);

what am I doing wrong??? I cant figure it out

  // 21.23 $
  int penny = 2123; // use what ever input you want                                            

  char *titles[] = {"10 dollar", "5 dollar", "1 dollar", "quarter", "dime", "penny"};
  int units[] = {1000, 500, 100, 25, 10, 1}; // in penny
  int i;

  for (i = 0; i < sizeof(units) / sizeof(int); i++){
    printf("%d * %s\n", penny / units[i], titles[i]);
    penny -= penny / units[i] * units[i];
  }

2 * 10 dollar
0 * 5 dollar
1 * 1 dollar
0 * quarter
2 * dime
3 * penny

On September 30 2012 10:27 tec27 wrote:

Well, that too, but I think that's a bit past his depth atm. The assignment is probably meant more to develop the greedy algorithm that fails in some cases, rather than the exact correct solution.

On September 30 2012 10:40 white_horse wrote:
yeah I'm in an introductory c++ class. I've studied on my own a little bit about arrays and stuff but we're not there yet in the class. I changed all the static_cast<float> to static_cast<int> and the program works for the bills but doesn't work for the coins. I know there must be something wrong with the calculation - can you guy help me find it...........

numPenny = static_cast<int>(total)*100 / (0.01*100);

numPenny = static_cast<int>(total / 0.01);

On September 30 2012 17:29 lolmlg wrote:
That explanation isn't really correct. The problem with the last version of his code was that the call to static_cast took place first. He wanted it to take place last. The line

static_cast<int>(1.07) * 100 / (0.10 * 100);

if it compiles (which it might not, if warnings are treated as errors) will yield the answer 10.0. In that example, all he would need to do in order to get the answer he wanted was surround the entire set of numeric operations with brackets, or use two static_cast calls to avoid the warning.

static_cast<int>(total * 100 / (0.10 * 100));
or
static_cast<int>(total) * 100 / static_cast<int>(0.10 * 100);

But then the question becomes, why bother with the multiplication? The operation can be reduced to the following:

static_cast<int>(total / 0.10);

Edit: Of course, this example didn't really apply to his program, because by the time he hit dimes, the amount of money should have been less than one, in which case the static_cast of total would have returned 0. So both the original line and the line with two static_cast calls would not have worked in his situation. The second line and the final one would be fine.

On September 30 2012 09:38 white_horse wrote:
Hey guys I'm working on this problem where the user inputs an amount of money between $0.00 and $19.99, and the program outputs the best way to calculate the change of that amount. So for example, if I put in "$9.94", then the program should output

One $5 bill
4 $1 bills
3 quarters
1 dime
1 nickel
4 pennies

I got this far

float total;
cout << "Input a dollar amount between 0.00 and 19.99 (inclusive): ";
cin >> total;

numTenDollar = static_cast<int>(total)*100 / (10*100);
numFiveDollar = static_cast<int>((total - numTenDollar))*100 / (5*100);
numOneDollar = static_cast<int>((total - numTenDollar - numFiveDollar))*100 / (1*100);

but the program is really weird when I run it and I think theres something wrong with the calculations. Can you guys help me out? Thanks.