This question already has answers here:
Using scanner.nextLine() [duplicate]
(5 answers)
Scanner issue when using nextLine after nextXXX [duplicate]
Closed 9 years ago.
I'm relatively new to programming and have recently started learning Java in order to move into Android programming. I thought I would create a very simple calculator to practice, but it seems that my if statement doesn't work.
import java.util.Scanner;
public class Calculator {
public static void main(String[] args) {
//Create new scanner object
Scanner numInput = new Scanner( System.in );
//Enter first number
System.out.println("Please enter the first number: ");
int num1 = numInput.nextInt();
//Enter the second number
System.out.println("Please enter the second number: ");
int num2 = numInput.nextInt();
//Choose the operation to perform (+,-,*,/)
System.out.println("What operation would you like to do?");
System.out.println("Type \"+\" to add.");
System.out.println("Type \"-\" to subtract.");
System.out.println("Type \"*\" to multiply.");
System.out.println("Type \"/\" to divide.");
String opChoice = numInput.nextLine();
//Add
if (opChoice.equals("+")) {
int ans = num1 + num2;
System.out.println("Adding " + num2 + " to " + num1 + " equals " + ans + ".");
}
//Subtract
else if (opChoice.equals("-")) {
int ans = num1 - num2;
System.out.println("Subtracting " + num2 + " from " + num1 + " equals " + ans + ".");
}
//Multiply
else if (opChoice.equals("*")) {
int ans = num1 + num2;
System.out.println("Multiplying " + num2 + " with " + num1 + " equals " + ans + ".");
}
//Divide
else if (opChoice.equals("/")) {
int ans = num1 + num2;
System.out.println("Dividing " + num1 + " by " + num2 + " equals " + ans + ".");
}
}
}
I am using the Eclipse IDE, and it runs fine until it asks for which operation to do. It will display the options but won't let me enter anything (I've been testing it with multiplying 5 by 2).
I searched for similar questions and tried what they suggested, but it still doesn't seem to work. I would appreciate any help, I assume this is probably just some simple error I am making, so I apologize if this seems like a silly question!
EDIT: Thanks for the quick responses, guys! I appreciate it. And yes, I fixed the multiply and division. :)
The problem is that nextInt() doesn't consume (doesn't read) the new-line character (that you input when you press [Enter]). One way to solve this is calling nextLine() after each nextInt():
//Enter first number
System.out.println("Please enter the first number: ");
int num1 = numInput.nextInt();
numInput.nextLine(); // Add this
//Enter the second number
System.out.println("Please enter the second number: ");
int num2 = numInput.nextInt();
numInput.nextLine(); // Add this
Another way to solve this, would be reading the numbers with nextLine() (which returns a String) and then parsing it to a int:
int num1 = Integer.parseInt(numInput.nextLine());
You won't need to add an extra nextLine() because the new-line character is being consumed by the nextLine() already called.
Also, as #sotondolphin suggested, you may want to check your * and / operations.
The issue is that when numInput.nextInt(); is called, you get the number entered ... but it leaves the newline (\n). Your call to numInput.nextLine(); then gets an empty string.
Replacing that call with numInput.next() will solve the problem as it has a slightly different behavior:
public String next()
Finds and returns the next complete token from this scanner. A complete token is preceded and followed by input that matches the delimiter pattern.
The default delimiter pattern is whitespace, which includes \n and what's in the input stream after you enter the operation (using * as example) is now \n*\n
The code below does addition but not expected multiplication and division. Could you please check the source?
//Multiply
else if (opChoice.equals("*")) {
int ans = num1 + num2;
System.out.println("Multiplying " + num2 + " with " + num1 + " equals " + ans + ".");
}
//Divide
else if (opChoice.equals("/")) {
int ans = num1 + num2;
System.out.println("Dividing " + num1 + " by " + num2 + " equals " + ans + ".");
}
}
Related
This question already has answers here:
How to clear the console?
(14 answers)
Closed last year.
I am making a CLI calculator and I am trying to add a clear button but cannot figure out how to clear all the user input and start the display from the beginning. I tried using the reset method and that didn't seem to do the trick.
System.out.println("Enter any of the following:");
System.out.println(" 1 2 3 4 5 6 7 8 9 ");
System.out.println(" + - * / = ");
System.out.println("Enter AC to reset ");
double firstNum = input.nextDouble();
input.nextLine();
if (input.equals(clear)) {
input.reset();
}
System.out.println("Display 1: " + firstNum);
System.out.println("Display 2: " + firstNum);
System.out.println("Operator: ");
String operand = input.nextLine();
System.out.println("Display 1: " + firstNum + " " + operand);
System.out.println("Display 2: " + firstNum );
if (operand.equals("=")) {
break;
}
System.out.println("Enter your next number: ");
double secondNum = input.nextDouble();
input.nextLine();
calculate(firstNum, operand, secondNum);
System.out.println("Display 1: " + firstNum + " " + operand + " " + secondNum );
firstNum = answer;
System.out.println("Display 2: " + answer);
}
System.out.println("Answer: " + answer);
}
I suppose it can't be done. I tried to solve the problem and this is a waste of time. If it helps, you can use special characters like "\b" to delete the previous character or "\r" to write from the beginning of the string. But when you press Enter, you can't change the previous line.
This is the code that I have so far. I just want to know if I'm correct. I am very new to this and most likely I'm correct but I still wanted to know. thanks
Scanner input = new Scanner(System.in);
//variables
int number1;
int number2;
System.out.println("enter first number: ");
number1 = input.nextInt();
System.out.println("enter first number: ");
number2 = input.nextInt();
int multiple = number1 % number2;
if((number1 % number2) == 0) {
System.out.println("Yes, " + number1 + " is a multiple of " + number2);
}
else {
System.out.println("No, " + number1 + " is not a multiple of " + number2);
}
System.out.println("The multiple is: " + multiple);
}
I guess you want if a number is divisible by other or not and want to get multiplier if so.
Scanner input = new Scanner(System.in);
//variables
int number1;
int number2;
System.out.println("enter first number: ");
number1 = input.nextInt();
System.out.println("enter second number: ");
number2 = input.nextInt();
if((number1 % number2) == 0) {
System.out.println("Yes, " + number1 + " is a multiple of " + number2);
System.out.println("The multiple is: " + (number1 / number2));
}
else {
System.out.println("No, " + number1 + " is not a multiple of " + number2);
}
Your code works fine. But if you consider couple of things here it would be good.
Change your second prompt to "enter second number"
Currently you are printing message "The multiple is: " every time whether you find multiple or not.
So print this message only when you found a multiple. Move this line to if block to achieve this.
I get this error; bad operand types for binary operator '-'
All other operations work...when I leave out the subtraction via comments like // and /* */; can someone help?
This is the code by the way; the exception is on the subtraction line.
public class Calculator {
/*
*use 'javac Calculator.java' to compile;
*use 'jar cvf Calculator.jar Calculator.class' for jar;
*use 'java Calculator' to run;
*/
public static void main(String []args) {
String NewName
Scanner user_input = new Scanner( System.in );
System.out.println("Type your name please.");
NewName = user_input.next();
System.out.println("");
System.out.println("Hello " + NewName + ".");
System.out.println("I am Hunter's java calculator program.");
System.out.println("");
//mathematical input
String operator;
float cal1, cal2;
System.out.println("Type a Number...");
cal1 = user_input.nextFloat();
System.out.println("");
System.out.println("Type another Number...");
cal2 = user_input.nextFloat();
System.out.println("");
Scanner opt = new Scanner(System.in);
System.out.println("Enter an operator");
operator = opt.next();
//operation decisions
if (operator.equals("+")){
System.out.println("The answer is " + cal1+cal2 + ".");
}
if (operator.equals("-")){
System.out.println("The answer is " + cal1-cal2 + ".");
}
if (operator.equals("/")){
System.out.println("The answer is " + cal1/cal2 + ".");
}
if (operator.equals("*")){
System.out.println("The answer is " + cal1*cal2 + ".");
}
}
}
You need parenthesis:
System.out.println("The answer is " + (cal1-cal2) + ".");
Otherwise what you have is treated as
System.out.println(("The answer is " + cal1) - (cal2 + "."));
which is invalid since you can't subtract strings.
Why don't you have an error with the other operators? Well, * and / have higher precedences, so those are working as expected. +, on the other hand, is overloaded to concatenate strings:
System.out.println("The answer is " + cal1+cal2 + "."); // concatenates, doesn't add
For example, if call1 is 1 and call2 is 2, the result will be:
The answer is 12.
which isn't what you want. Again, this can be solved with parenthesis.
I am attempting to simplify my long code of a calculator program, but I have a road block. I have a new else if statement for each calculator operator, but what I want to do is allow the user to manually type in, on one line, the entire operation they would like to perform and have the code compute it.
Here's what I have:
do {
System.out.println("What function would you like to perform?");
System.out.print("Exit Calculator (Q), Add (+), Subtract (-), Multiply (x), Divide (/): ");
maininput = in.next();
if (maininput.equals("+")) {
System.out.print("Enter the first number to add: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to add: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 + num2;
System.out.println(num1 + " + " + num2 + " = " + answer);
System.out.println();
}
else if (maininput.equals("-")) {
System.out.print("Enter the first number to subtract: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to subtract: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 - num2;
System.out.println(num1 + " - " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("x")) {
System.out.print("Enter the first number to multiply: ");
num1 = in.nextDouble();
System.out.print("Enter the second number to multiply: ");
num2 = in.nextDouble();
System.out.println();
answer = num1 * num2;
System.out.println(num1 + " x " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("/")) {
System.out.print("Enter the first number to divide: ");
num1 = in.nextDouble();
do {
System.out.print("Enter the second number to divide: ");
num2 = in.nextDouble();
System.out.println();
if (num2 == 0) {
System.out.println("Cannot divide by 0! Please enter a different number.");
}
} while (num2 == 0);
answer = num1 / num2;
System.out.println(num1 + " / " + num2 + " = " + answer);
System.out.println();
}
else if(maininput.equals("Q") || maininput.equals("q") || maininput.equals("EXIT") || maininput.equals("exit")) {
in.close();
System.exit(0);
}
else {
System.out.println(maininput + " is not a valid operand. Please try again.");
System.out.println();
}
} while (maininput != "Q" && maininput != "q");
This is what I want the output to be:
Enter operation:
4 * 6
4 * 6 = 24
Should be able to enter any operation here on one line. I am not asking you to write my calculator for me, I am asking how to allow the computer to read in the entire operation off one line and compute it, then print it.
If you use scanner readLine then you can read a whole line
e.g.
4 * 6
This line can then be split to get three tokens
String tokens [] = line.split (" ");
then you can see what operation to do based upon token[1]
if (token[1].equals ("-") {
//lets minus token[2] from token[0]
// need to convert String to Number
}
You can use String.split and store it in an array. Then it will return an array of string, parse those back to integers. the do the operation you want. The x variable will be the result.
if(maininput.contains("+")) {
String[] stringarr = string.split("\\+");
int x = Integer.parseInt(stringarr[0]) + Integer.parseInt(stringarr[1]);
System.out.println(stringarr[0] + " + " + stringarr[1] + " = " + x);
} else if(maininput.contains("-")) {
String[] stringarr = string.split("\\-");
int x = Integer.parseInt(stringarr[0]) - Integer.parseInt(stringarr[1]);
System.out.println(stringarr[0] + " - " + stringarr[1] + " = " x);
}
... And so on.
You could try parsing the line using a Pattern object, something like this:
Pattern opPattern = Pattern.compile("(\\d+) *([+-*/]) *(\\d+)");
Matcher matcher = opPattern.matcher(userLine);
if(matcher.find()) {
int op1 = Integer.toValue(matcher.group(1));
int op2 = Integer.toValue(matcher.group(3));
String op = matcher.group(2);
if(op.equals("+")) {
// do + op ...
} else ... {
// etc...
}
} else {
// error in line, not the form of an operation
}
Have a look at the javadoc, as I'm not sure if I used the correct method names and the like, just tried to illustrate the idea...
This program is designed to add 2 random numbers generated by the computer, when the user answer goes wrong , the computer tells the user to try it again, by using the while loop. The program will stop once the user enters a correct number. I have to calculate the wrong count in the while loop, however, it gives me the wrong count 1 when it is the second attempt.Please be kind enough to tell me where I go wrong in the code. Thank you.
import java.util.Scanner;
public class add {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int num1 = (int) (Math.random() * 10);
int num2 = (int) (Math.random() * 10);
int wrong = 0;
System.out.println("What is " + num1 + "+" + num2 + "=" + "?");
int answer = input.nextInt();
while (num1 + num2 != answer) {
System.out.println("Wrong answer, Try again . " +
"What is " + num1 + "+" + num2 + "? ");
answer = input.nextInt();
System.out.println("The number of attemt is " + wrong);
++wrong;
}
System.out.println("You got it correct !");
}
}
The error is in incrementing the number the user has gotten wrong AFTER printing "You got x wrong"
Just put ++wrong above System.out.println("The number of attemt is " + wrong);
while (num1 + num2 != answer) {
System.out.println("Wrong answer, Try again . " +
"What is " + num1 + "+" + num2 + "? ");
answer = input.nextInt();
++wrong;
System.out.println("The number of attemt is " + wrong);
}
Just change
wrong = 0
to
wrong = 1
wrong should probably be renamed to numberOfAttempts.
Initialize wrong to 1 instead of 0.
int wrong = 1;
A more appropriate name for the variable would be attempt if you take this approach.
You need to increment wrong before you display it:
import java.util.Scanner;
public class Add {
public static void main(String[] args ){
Scanner input = new Scanner (System.in);
int num1 = (int)(Math.random() * 10);
int num2 = (int)(Math.random() * 10);
int wrong = 0 ;
System.out.println("What is " + num1 + "+" + num2 + "=" + "?");
int answer = input.nextInt();
while (num1 + num2 != answer){
wrong++ ;
System.out.println("Wrong answer, Try again . What is " + num1 +"+"+ num2 + "? " );
answer = input.nextInt();
System.out.println("The number of attempt is " + wrong);
}
System.out.println("You got it correct !");
}
}