Please help me fix the error

Question

I am not done with the program but I get errors that I am not sure how to fix them. I was wondering if anyone can help me solve the problem.
This program is a quiz program and has to handle 3 subjects. The user is able to select from these 3 categories. The program presents 3 questions and has to provide 4 option for each question. One would be to exit from the quiz. If the user responds to a question correctly, the program displays a positive feedback message. If the user responds incorrectly to the question, the program displays the correct answer. Exiting the questions menu returns the student to the topics menu. At the end of the quiz, the program displays the total number of correct and incorrect answers for each topic. Have a counter to count the correct answers.
Plese help me fix the problem with the code
import java.util.Scanner;
import java.io.*;
public class Test
int correctAnswer = 0;
String str;
String q;
Scanner scan = new Scanner (System.in);
System.out.println("key in m for Math category, s for Science category, a for Art category, or x to exit the test");
String str = scan.nextLine();
while (str != 'x')
if( str == m)
System.out.println (" What is the area if Triangle? a) l*W b)S^2 c)1/2 b * h");
q = scan.nextLine();
if (q == c)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("What is the premiter? a)The distance of all the sides b)the parallel distance c)The angle of a shape");
q = scan.nextLine();
if (q == a)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("What is a right angle? a)100 degree b)180 degree c)90 degree");
q = scan.nextLine();
if (q == c)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
if( str == s)
System.out.println (" What is Diffusion? a)No movement between Molecules b)Movement of molecules high to low c)Movement of molecules high to low");
q = scan.nextLine();
if (q == c)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("What is the element sign for carbon dioxide? a)CO2 b)CO c)O2");
q = scan.nextLine();
if (q == a)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("What is the normal body temperature? a)98.5 b)99.0 c)102.1");
q = scan.nextLine();
if (q == a)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
if( str == a)
System.out.println ("which artist painted the Monalisa? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso ");
q = scan.nextLine();
if (q == a)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("which artist painted the Sister Chapple? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso ");
q = scan.nextLine();
if (q == a)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
System.out.println ("which artist paint the Monalisa? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso");
q = scan.nextLine();
if (q == b)
System.out.println(" your answer is correct");
correctAnswer = correctAnswer+1
else System.out.println(" your answer is not correct");
}}

Answer 1

Here's a better version, fixing what I mentioned above. I haven't test compiled it, but it should work now. As a note, you might want to look into the ++ operator as well. And when you post code, enclose it in the "code" tags (see the code button above your posting). That makes it easier to read.
Anyway, here it is:
import java.util.Scanner;
import java.io.*;
public class Test {
     int correctAnswer = 0;
     String str;
     String q;
     Scanner scan = new Scanner (System.in);
     static public void main(String [] args) {
          System.out.println("key in m for Math category, s for Science category, a for Art category, or x to exit the test");
          String str = scan.nextLine();
          while (!str.equals("x")) {
               if( str.equals("m")) {
                    System.out.println (" What is the area if Triangle? a) l*W b)S^2 c)1/2 b * h");
                    q = scan.nextLine();
                    if (q.equals("c")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                          System.out.println(" your answer is not correct");
                    System.out.println ("What is the premiter? a)The distance of all the sides b)the parallel distance c)The angle of a shape");
                    q = scan.nextLine();
                    if (q.equals("a")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                          System.out.println(" your answer is not correct");
                    System.out.println ("What is a right angle? a)100 degree b)180 degree c)90 degree");
                    q = scan.nextLine();
                    if (q.equals("c")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else { System.out.println(" your answer is not correct");
               if( str.equals("s")) {
                    System.out.println (" What is Diffusion? a)No movement between Molecules b)Movement of molecules high to low c)Movement of molecules high to low");
                    q = scan.nextLine();
                    if (q.equals("c")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                         System.out.println(" your answer is not correct");
                    System.out.println ("What is the element sign for carbon dioxide? a)CO2 b)CO c)O2");
                    q = scan.nextLine();
                    if (q.equals("a") {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                         System.out.println(" your answer is not correct");
                    System.out.println ("What is the normal body temperature? a)98.5 b)99.0 c)102.1");
                    q = scan.nextLine();
                    if (q.equals("a")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                         System.out.println(" your answer is not correct");
               if( str.equals("a")) {
                    System.out.println ("which artist painted the Monalisa? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso ");
                    q = scan.nextLine();
                    if (q.equals("a")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                         System.out.println(" your answer is not correct");
                    System.out.println ("which artist painted the Sister Chapple? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso ");
                    q = scan.nextLine();
                    if (q.equals("a")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                          System.out.println(" your answer is not correct");
                    System.out.println ("which artist paint the Monalisa? a)Michael Angelo b)Leonardo De Vinci c)Pablo Picasso");
                    q = scan.nextLine();
                    if (q.equals("b")) {
                         System.out.println(" your answer is correct");
                         correctAnswer = correctAnswer+1;
                    } else {
                         System.out.println(" your answer is not correct");
}