java - Stopping a repeating Println in a while loop, BlueJ -

below code have far, calculator computer science class. problem having on second run of program system.out.print("would perform calculation? (y/n) "); runs twice instead of once. have turned in project, know why , how, in future programs, can fix it. i'll post rest of code below.

i appreciate of help, credit "a" got on of you. thanks!

/** * calculator multiple functions. * @author ()  * @version (version 2.1) */ import java.io.*; import java.util.scanner; public class calc {   public static void main(string args[])   {     scanner reader = new scanner(system.in);     string cont = "", funct = "";     double fnum = 0, snum = 0, answer = 0;      while(true)     {         system.out.print("would perform calculation? (y/n) ");         cont = reader.nextline();         if (cont.equalsignorecase("y"))         {             system.out.println("what function do?");             system.out.println("+?");             system.out.println("-?");             system.out.println("*?");             system.out.println("/?");             funct = reader.nextline();             if (funct.equals("+"))             {                 system.out.println("simple addition calculator");                 system.out.println("enter first num: ");                 fnum = reader.nextdouble();                 system.out.println("enter second num: ");                 snum = reader.nextdouble();                 answer = fnum + snum;                 system.out.println("answer: " + answer);                 system.out.println(" ");             }             if (funct.equals("-"))             {                  system.out.println("simple subtraction calculator");                 system.out.println("enter first num: ");                 fnum = reader.nextdouble();                 system.out.println("enter second num: ");                 snum = reader.nextdouble();                 answer = fnum - snum;                 system.out.println("answer: " + answer);                 system.out.println(" ");             }             if (funct.equals("*"))             {                  system.out.println("simple multiplication calculator");                 system.out.println("enter first num: ");                 fnum = reader.nextdouble();                 system.out.println("enter second num: ");                 snum = reader.nextdouble();                 answer = fnum * snum;                 system.out.println("answer: " + answer);                 system.out.println(" ");             }             if (funct.equals("/"))             {                  system.out.println("simple division calculator");                 system.out.println("enter first num: ");                 fnum = reader.nextdouble();                 system.out.println("enter second num: ");                 snum = reader.nextdouble();                 answer = fnum / snum;                 system.out.println("answer: " + answer);                 system.out.println(" ");             }         }         else if (cont.equalsignorecase("n"))         {             break;         }      }   } } 

in of function conditions inside loop, using reader.nextdouble(). read number (e.g "8") input not new line (the enter) entered user after number. following code minus(-) function not print "would perform calculation? (y/n) " twice new line read. here reader.nextline() used instead of reader.nextdouble(). reader.nextline() read whole line not number.

if (funct.equals("-"))         {             system.out.println("simple subtraction calculator");             system.out.println("enter first num: ");             fnum = double.parsedouble( reader.nextline());             system.out.println("enter second num: ");             snum = double.parsedouble( reader.nextline());             answer = fnum - snum;             system.out.println("answer: " + answer);             system.out.println(" ");         }