Exercise that prints the cell phones' bills. Please help.

**andreas90** · January 4th, 2012, 07:11 PM

This is a part from the code of my application. With the following method i want to calculate the cost of each call. Each call "belongs" to a service. So i call the method in main with argument the phone number of the service. The problem (specified with red color) is that i cannot calculate the cost correctly for the first call that overtakes the free time.
For example, the free time is 30 min and 0,1 cost for every additional minute. The first call lasts 15 min and the second 20. The result must be: for the first call, cost 0, and for the second, cost 0,1*5=0,5.

public void printCalls(String num) 
        {
            double j = 0;  /* total duration */
            double y = 0; /* cost of each call*/
 
            for(int i=0; i<Call.calls.size();i++)  /* for every call */
                {
			if (Call.calls.get(i).getCallingNumber().equals(num))
                             /* if the calling number equals the service's number */
                            {    
 
                                j+= Call.calls.get(i).getCallingDuration();
                                /* increase j by duration of call*/
 
                                if (j <= 30*60)    /* if j < free calling time*/
                                    {
                                        y = 0;
                                    }
                              else y = Call.calls.get(i).getCallingDuration()*0.11;
                                           System.out.printf  
                                            ("%s. %s: %s %s: %s %s: %s %s %s: %s’’ %s: %.2f€\n",
                                            "Call" , "From" , Call.calls.get(i).getCallingNumber() ,
                                            " To" ,  Call.calls.get(i).getDialedNumber(),
                                            " Time" , Call.calls.get(i).getCallingDate(),Call.calls.get(i).getCallingTime(),
                                            " Duration" , Call.calls.get(i).getCallingDuration() ,
                                            " Cost" , y);                     
                            }          
		}
        }

I think the solution would be something like this (in pseudocode):

if  total duration <= free duration
    cost = 0;
 
else 
   {
      if total duration [B][U]of the previous iteration (i-1)[/U][/B] <= free duration
          cost = (duration - (free duration - total duration of the previous iteration) )* cost         
 
      else duration * cost
      }

But the problem is that i don't know how to get the value of total duration of the previous iteration.
Any Suggestions?

**Norm** · January 4th, 2012, 08:18 PM

i cannot calculate the cost correctly for the first call that overtakes the free time.

Are you saying that you need more logic than can be done in a single statement like your statement in red? What keeps you from getting the time as a variable and then using some if statements and arithmetic statements to break the time into the different chargeable times?

Take a piece of paper and work out the steps for breaking the time up for the different charges.
You need to understand how to do it with paper and pencil before you can write the code.

**andreas90** · January 5th, 2012, 05:11 AM

Originally Posted by Norm

Are you saying that you need more logic than can be done in a single statement like your statement in red? What keeps you from getting the time as a variable and then using some if statements and arithmetic statements to break the time into the different chargeable times?

Take a piece of paper and work out the steps for breaking the time up for the different charges.
You need to understand how to do it with paper and pencil before you can write the code.

I 've done it and ended up with the solution that's been written in the end of the thread. I 've got all the variables i need, but i cannot find a way to retrieve the value of the total duration from the previous iteration, which i wanna use in my if statements

**Norm** · January 5th, 2012, 06:17 AM

a way to retrieve the value of the total duration from the previous iteration

What do you mean by "the previous iteration"?
In a loop you would have a variable that saves the value from the previous iteration:

int lastValue = -1;  // will save value here
for(....)  {
  value = (some formula)
   ... here lastValue if != -1 is the value from the previous iteration
   lastValue = value; // save this value for the next iteration
} // end for loop

**andreas90** · January 5th, 2012, 07:42 AM

Thanks a lot Norm! Problem solved!

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