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cannot find symbol error in condition of while loop

I'm writing a program for an assignment that should give random problems for the user to solve. what I am attempting to make it do is after selecting a problem type and answering one question the program should load the menu up again.
Originally I wrote a method that would be called in the else statement on line 147. The method successfully looped however the assignment specifically asks for a loop to make it happen. I've tried several different ways to change the loops condition statement but I'm not sure where I went wrong? any help would be appreciated.
I want very badly to use a switch statement but I can't as we haven't learned that in class.
// Importing Scanner and Random class for later.
import java.util.Scanner;
import java.util.Random;
class AlgebraTutor {
// Solve for Y method.
public static void solve_for_y() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_m = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_b = number_gen.nextInt(101) - 100;
// Print problem out for student to see
System.out.println("Problem: y = " + var_m + "(" + var_x +")" + "+" + var_b);
System.out.println(" m =" + var_m);
System.out.println(" x =" + var_x);
System.out.println(" b =" + var_b);
// This formula will calculate the value of y.
float var_y = (var_m * var_x) + var_b;
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for y:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_y){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_y);
}
}
// -------------------------------------------------------------------------
// Solve for M method.
public static void solve_for_m() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_y = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_b = number_gen.nextInt(101) - 100;
// Print problem out for student to see.
System.out.println("Problem: " + var_y + " = m (" + var_x +") + " + var_b);
System.out.println(" y =" + var_y);
System.out.println(" x =" + var_x);
System.out.println(" b =" + var_b);
// This formula will calculate the value of m.
float var_m = (var_y - var_b) / var_x;
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for m:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_m){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_m);
}
}
// -------------------------------------------------------------------------
// Solve for B method
public static void solve_for_b() {
// Creation of a random number generator.
Random number_gen = new Random();
// Generates random integers from -100 to 100.
int var_y = number_gen.nextInt(101) - 100;
int var_x = number_gen.nextInt(101) - 100;
int var_m = number_gen.nextInt(101) - 100;
// Print problem out for student to see.
System.out.println("Problem: " + var_y + " = " + var_m + " (" + var_x +") " + "+ b");
System.out.println(" y =" + var_y);
System.out.println(" x =" + var_x);
System.out.println(" m =" + var_m);
// This formula will calculate the value of m.
float var_b = var_y / (var_m * var_x);
// Using the scanners class a scanner object called userInput was created to record students answer. Answer was taken as a string and converted to an integer.
Scanner user_input = new Scanner(System.in);
System.out.println("Please solve for b:");
String user_answer = user_input.nextLine();
int answer = Integer.parseInt(user_answer);
if (answer == var_b){
System.out.println("correct");
}else{
System.out.println("incorrect, The answer is:" + var_b);
}
}
// -------------------------------------------------------------------------
public static void main(String[] args) {
do{
System.out.println("Which type of problem would you like to practice?");
System.out.println("1) Solve for y");
System.out.println("2) Solve for m");
System.out.println("3) Solve for b");
System.out.println("4) To quit");
Scanner selection_input = new Scanner(System.in);
String user_selection = selection_input.nextLine();
if ( user_selection.equals("1")){
solve_for_y();
} else if (user_selection.equals("2")){
solve_for_m();
} else if (user_selection.equals("3")){
solve_for_b();
} else if (user_selection.equals("4")){
System.out.println("Quitting Program");
System. exit(0);
} else{
System.out.println("Please choose from the given options");
}
} while(user_selection.equals("1") &&
user_selection.equals("2") &&
user_selection.equals("3") &&
user_selection.equals("4"));
}
}

You must declare the user_inpout variable outside the do...while loop, then you can check its value in the while() expression. Also you should initialize the scanner only once at the beginning of your program.
public static void main(String[] args)
{
Scanner selection_input = new Scanner(System.in);
String user_selection=null;
do
{
System.out.println("Which type of problem would you like to practice?");
System.out.println("1) Solve for y");
System.out.println("2) Solve for m");
System.out.println("3) Solve for b");
System.out.println("4) To quit");
user_selection = selection_input.nextLine();
if (user_selection.equals("1"))
{
solve_for_y();
}
else if (user_selection.equals("2"))
{
solve_for_m();
}
else if (user_selection.equals("3"))
{
solve_for_b();
}
else if (user_selection.equals("4"))
{
System.out.println("Quitting Program");
System.exit(0);
}
else
{
System.out.println("Please choose from the given options");
}
}
while (!user_selection.equals("4"));
}
For the case "4" you have two exists now:
else if (user_selection.equals("4"))
{
System.out.println("Quitting Program");
System.exit(0);
}
and:
while (!user_selection.equals("4"));
Only one of both is needed. So you may either remove the first one or replace the while statement by while(true).

simple command line stock control

I want to develop a command line solution for a supermarket to calculate the total of the customer's purchase and display it and after every customer's purchase the initial stock of all the items must be updated.(I've used only 3 items).But it's only calculating the total not updating the stock.(And I need to do it by using while loops & for loops only
import java.util.*;
public class newClass {
public static void main(String args[]){
int qty1=100;
int qty2=200;
int qty3=300;
float price1=50.0f;
float price2=50.0f;
float price3=100.0f;
Scanner sc=new Scanner(System.in);
System.out.println("Input item1 quantity");
int no1=sc.nextInt();
System.out.println("Input item2 quantity");
int no2=sc.nextInt();
System.out.println("Input item3 quantity");
int no3=sc.nextInt();
float total=(no1*price1)+(no2*price2)+(no3*price3);
while(qty1>=no1 & qty2>=no2 & qty3>=no3 )
{
qty1=qty1-no1;
qty2=qty2-no2;
qty3=qty3-no3;
}
System.out.println("your total is="+total);
}
}

There are lots of issue with your code. Firstly you intend to loop based on the in-house initial quantity but are not looping it on it. After updating quantity, you need to ask input from the user again if you have given quantity. You are not closing the Scanner object properly.
Below is modified version of your code. Hope this helps
public static void main(String args[]) {
int qty1 = 100;
int qty2 = 200;
int qty3 = 300;
float price1 = 50.0f;
float price2 = 50.0f;
float price3 = 100.0f;
Scanner sc = new Scanner(System.in);
while (qty1 > 0 && qty2 > 0 && qty3 > 0) { // You any of the quantity is out of stock, exit loop
System.out.println("\nCurrent Stock: qty1: " + qty1 + " qty2: " + qty2 + " qty3: " + qty3 + "\n");
System.out.println("Input item1 quantity");
int no1 = sc.nextInt();
System.out.println("Input item2 quantity");
int no2 = sc.nextInt();
System.out.println("Input item3 quantity");
int no3 = sc.nextInt();
if (qty1 < no1) { // making sure that asked quantity is not more that in-house quantity
no1 = qty1;
}
if (qty2 < no2) {
no2 = qty2;
}
if (qty3 < no3) {
no3 = qty3;
}
qty1 = qty1 - no1;
qty2 = qty2 - no2;
qty3 = qty3 - no3;
float total = (no1 * price1) + (no2 * price2) + (no3 * price3);
System.out.println("your total is=" + total);
}
sc.close();
}

How do I show the numbers I entered in Java

I'm writing a program where at the end I have to display the numbers I entered and the maximum and minimum of those entered numbers. However I'm running into a little problem, here is my code,
import java.util.*;
public class question3controlstructures {
public static void main (String [] args) {
Scanner in = new Scanner (System.in);
int numberEntered;
int numbersinput = 0;
String answer ="";
double sum = 0;
do {
System.out.println("Enter a number");
numberEntered = in.nextInt();
numbersinput ++;
System.out.println("do you want to enter another number?");
answer = in.next();
sum = sum + numberEntered;
} while (answer.equals("yes"));
System.out.println("The sum is: " + sum);
System.out.println("The average is: " + sum/numbersinput);
System.out.println(numberEntered);
}
}

The above comment are absolutely useful. However, here is little code
package com.mars;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
public class Question3controlstructures {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList<Integer>();
System.out.print("Enter integers please ");
System.out.println("(EOF or non-integer to terminate): ");
while (scan.hasNextInt()) {
list.add(scan.nextInt());
}
Integer[] nums = list.toArray(new Integer[0]);
int sum = 0;
int i = 0;
for ( ; i < nums.length; i++) {
sum = sum + nums[i];
}
System.out.println("sum..." + sum);
System.out.println("The average is: " + sum / i);
System.out.println(i);
System.out.println("max.. "+Collections.max(list));
System.out.println("min.. "+Collections.min(list));
scan.close();
}
}
As suggent in comments , you need a list to store the multiple numbered entered.

just compare the min and max every time you enter a number
int min = Integer.MAX_VALUE
int max = Integer.MIN_VALUE
int numberEntered;
int numbersinput = 0;
String answer ="";
double sum = 0;
do {
System.out.println("Enter a number");
numberEntered = in.nextInt();
System.out.println("YOU HAVE ENTERED: " + numbersEntered);
if (min > numberEntered) min = numberEntered;
if (max < numberEntered) max = numberEntered;
numbersinput ++;
sum = sum + numberEntered;
System.out.println("do you want to enter another number?");
answer = in.next();
} while (answer.equals("yes"));
System.out.println("The sum is: " + sum);
System.out.println("The average is: " + sum/numbersinput);
System.out.println(numberEntered);
//you can print your min max here.

The IntSummaryStatistics class together with Java 8's Stream API may be less verbose than dealing with min, max, sum and avg calculation manually.
public static void main(String[] args) {
// Get user input.
List<Integer> numbers = new ArrayList<>();
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
// No user friendly way to gather user input, improve!
numbers.add(scanner.nextInt());
}
// Transform input to statistics.
IntSummaryStatistics stats = numbers.stream()
.collect(Collectors.summarizingInt(Integer.intValue()));
// Print statistics.
String jointNumbers = numbers.stream()
.collect(Collectors.joining(", "));
System.out.printf("You entered %d numbers: %s\n, stats.getCount(), jointNumbers);
System.out.println("Min: " + stats.getMin());
System.out.println("Max: " + stats.getMax());
System.out.println("Sum: " + stats.getMax());
System.out.println("Avg: " + stats.getAverage());
}

Brand new to Java, need some help restarting a while loop

I have just started learning Java in the last week or so and I'm creating a program that acts as a sales calculator that calculates commission.
My code is as follows:
import java.util.Scanner;
public class Application {
int itemOne;
int itemTwo;
int itemThree;
int itemFour;
final double baseCommission = 200;
final double itemOnePrice = 239.99;
final double itemTwoPrice = 129.75;
final double itemThreePrice = 99.95;
final double itemFourPrice = 350.89;
final double commissionPercentage = 0.09;
boolean startLoop = false;
public void start(){
while (startLoop = false);
{
//Welcome message
System.out.println("Welcome to Devon's Sales Calculator!");
//Defining new scanner
Scanner user_input = new Scanner(System.in);
//Getting user input for salesperson name along with number of items sold as well as assigning them to a variable
String salesman_name;
System.out.print("Insert salesperson name:\t");
salesman_name = user_input.next();
System.out.print("Enter number of first item sold:\t");
int first_item = user_input.nextInt();
System.out.print("Enter number of second item sold:\t");
int second_item = user_input.nextInt();
System.out.print("Enter number of third item sold:\t");
int third_item = user_input.nextInt();
System.out.print("Enter number of fourth item sold:\t");
int fourth_item = user_input.nextInt();
//Printing out the name of the salesmen, followed by the total price of items sold
System.out.println("Sales Person\t" + salesman_name);
System.out.println("Total price of first item sold\t" + first_item * itemOnePrice);
System.out.println("Total price of second item sold\t" + second_item * itemTwoPrice);
System.out.println("Total price of third item sold\t" + third_item * itemThreePrice);
System.out.println("Total price of fourth item sold\t" + fourth_item * itemFourPrice);
//Calculating total of all items sold
double finalPrice = first_item * itemOnePrice + second_item * itemTwoPrice + third_item * itemThreePrice + fourth_item * itemFourPrice;
//Calculating commission # 0,9%
System.out.println("Total commission earned\t" + finalPrice * commissionPercentage);
//Decision whether or not to restart the while loop
String decision;
System.out.println("Would you like to check another salesperson?");
decision = user_input.next();
if(decision == "yes"){
startLoop = false;
}
else if(decision == "no"){
startLoop = true;
}
}
}
}
Whenever I execute my while loop, it doesn't restart to choose another salesman. I'm probably doing something horribly wrong and my code formatting is probably horrible. Any help would be appreciated.

Get rid of the = false and the semicolon. So not:
while (startLoop = false);
{
System.out.println("foo");
}
which is equivalent to
while (startLoop = false) {
// do nothing
}
{
System.out.println("foo");
}
Instead do,
while (!startLoop) {
// do something here
}

Code seems to skip over if or for loop

When I enter input that satisfies everything and doesn't trigger any of my errors, the program just exits after last input like it is skipping over the for or if loop.
Also after System.out.printf("Enter the name of your second species: "); it won't allow for any input, it just skips to the next prompt. I'm not sure why that is. The section above it asking for the first species' info works fine.
import java.util.Scanner;
public class HW2johnson_pp1 {
public static void main(String args[]) {
Scanner keyboard = new Scanner(System.in);
System.out.printf("Please enter the species with the higher" +
" population first\n");
System.out.printf("Enter the name of your first species: ");
String Species1 = keyboard.nextLine();
System.out.printf("Enter the species' population: ");
int Pop1 = keyboard.nextInt();
System.out.printf("Enter the species' growth rate: ");
int Growth1 = keyboard.nextInt();
System.out.printf("Enter the name of your second species: ");
String Species2 = keyboard.nextLine();
System.out.printf("Enter the species' population: ");
int Pop2 = keyboard.nextInt();
System.out.printf("Enter the species' growth rate: ");
int Growth2 = keyboard.nextInt();
if (Pop2 > Pop1) {
System.out.printf("The first population must be higher. \n");
System.exit(0);
}
Species input1 = new Species();
input1.name = Species1;
input1.population = Pop1;
input1.growthRate = Growth1;
Species input2 = new Species();
input2.name = Species2;
input2.population = Pop2;
input2.growthRate = Growth2;
if ((input1.predictPopulation(1) - input2.predictPopulation(1)) <=
(input1.predictPopulation(2) - input2.predictPopulation(2))){
System.out.printf(Species2 + " will never out-populate " +
Species1 + "\n");
}
else {
for (int i = 0; input2.predictPopulation(i) <=
input1.predictPopulation(i); i++) {
if (input2.predictPopulation(i) == input1.predictPopulation(i)) {
System.out.printf(" will out-populate \n");
}
}
}
}
}
This for the predictPopulation():
public int predictPopulation(int years)
{
int result = 0;
double populationAmount = population;
int count = years;
while ((count > 0) && (populationAmount > 0))
{
populationAmount = (populationAmount +
(growthRate / 100) * populationAmount);
count--;
}
if (populationAmount > 0)
result = (int)populationAmount;
return result;
}

This is because you never print anything after Species 2 overtakes Species 1, except in the very special case that Species 2 and Species 1 have exactly the same population in some year.
This is because, when you enter Species 1's growth rate, you enter an integer, and then press Enter. keyboard.nextInt() swallows the integer, but leaves the newline on the input-buffer, so the subsequent keyboard.nextLine() thinks there's an empty line there waiting for it.