How to calculate Cell phone bill in java, calculation issues -

my task calculate monthly cell phone bill in java, new java , still learning. can't seem understand calculations , how there. have named variables , constants , initiliazed them, need make calculations find cost of total bill. output i'm trying reach : run: minutes used = 675 text messages sent/recieved = 1031 data used = 605 megabytes. have data play? (y/n) : y have text message plan (y/n)?: y monthly cell phone charges : monthly plan = 39.99 text message plan = 15.00 data plan = 20.00 addidtional minutes charged = 79.85 charge data overage = 40.00

public static void main(string[] args) {         // todo code application logic here         scanner user_input = new scanner(system.in);          final double monthly_plan_voice;         final int allowable_minutes;         final double additional_minute_rate;         final double text_msg_plan;         final double text_msg_rate;         final double data_plan_rate;         final int allowable_data_incr;          monthly_plan_voice = 39.99; //double cause of decimal         allowable_minutes = 500; // int because no need decimal         additional_minute_rate = 0.45; // has decimal          text_msg_plan = 15.00; // rate depending on user input(double)         text_msg_rate = 0.12; // rate depending on user input (double)         data_plan_rate = 20.00; // double cause of decimal         allowable_data_incr = 300; //int cause increment          string minutes;         system.out.print("enter number of minutes used month: ");         minutes = user_input.next();         string texts;         system.out.print("do have text message plan? (y/n): ");          texts = user_input.next();         system.out.print("enter number of sent , recieved texts: ");         texts = user_input.next();         string data;         system.out.print("do have data plan? (y/n): ");         data = user_input.next();         system.out.print("enter amount of data used: ");         data = user_input.next();            if (allowable_data_incr < 300)          {         system.out.print("the cost of data 20.00$ ");         }         else          {             system.out.println("the cost of data 40.00$" );         }           if (allowable_minutes > 500)         {         system.out.print("");         } 

first personal option keep code clean , initiate , assign in 1 step:

 final double monthly_plan_voice = 39.99; //double cause of decimal 

secondly dollar sign "$" should used prefix number. ex $5.99 print statement reads:

 system.out.print("the cost of data 20.00$ "); 

i recommend changing each of little more professional.

 system.out.print("the cost of data $20.00."); 

now answer question. find total create new variable of type double. :

double totalmonthlybill = 0; 

now in each of if else statements add cost per each part of bill total variable.

for example:

 if (allowable_data_incr < 300)      {     system.out.print("the cost of data 20.00$ ");     totalmonthlybill += 20;     }     else      {         system.out.println("the cost of data 40.00$" );     totalmonthlybill += 40;     } 

the += add or subtract if negative value of (totalmonthlybill) whatever passed. can use += 2 variable or passing int or double ext.

assuming variable1 , variable2 initialized , both have been given value of not null

variable1 += variable2; variable1 += 2; 

this same as:

variable1 = variable1 + variable2; variable1 = variable1 + 2; 

but in case since have running total , defining cost based of each step can achived defining total variable , using += in each if/else statement add value total can call later final price

system.out.println("total monthly bill: " + totalmonthlybill); 

hope solves problem.