How can I take input as a string and convert to an integer stored in a seperate class?

I am trying to have the user input a letter grade and then convert it to an integer that is stored in a separate public class. I used several if loops to try to make this happen, but I can't get it to work. Any ideas what I am doing wrong and how to fix or work around it? When I run the code how it is now, all I can get for output is 0. I have a feeling that this is probably because I am trying to store the value in a separate class, but I don't know how to make it work.

import java.util.Scanner;
class Courses {
static public String letterGrade;
static public int numberGrade;
static public int creditValue;
static public float GPA;
}
public class GradeCruncher {
static Scanner userinput = new Scanner(System.in);
public static void main(String[] args) {
int numOfCourses;
int courseNum = 0;
System.out.println("How many courses would you like to input?");
numOfCourses = userinput.nextInt();
Courses[] course = new Courses[numOfCourses];
while (courseNum < numOfCourses) {
System.out.println("Enter info for course " + courseNum);
System.out.println("How many credits is this course worth?");
course[courseNum].creditValue = userinput.nextInt();
System.out.println("What is your current letter grade for this course?");
userinput.next();
course[courseNum].letterGrade = userinput.nextLine();
String aPlus = "a+", a = "a", aMinus = "a-", bPlus = "b+", b = "b", bMinus = "b-", cPlus =          "c+", c = "c",
cMinus = "c-", dPlus = "d+", d = "d", dMinus = "d-", f = "f";
if (f.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 0;
}
else if (dMinus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 60;
}
else if (d.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 63;
}
else if (dPlus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 67; 
}
else if (cMinus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 70;
}
else if (c.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 73;
}
else if (cPlus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 77;
}
else if (bMinus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 80;
}
else if (b.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 83;
}
else if (bPlus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 87;
}
else if (aMinus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 90;
}
else if (a.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 93;
}
else if (aPlus.equalsIgnoreCase(Courses.letterGrade)) {
course[courseNum].numberGrade = 100;
}
System.out.println(course[courseNum].numberGrade);
courseNum++;
continue;
}
System.out.println(course[courseNum].numberGrade);
Courses.GPA = ((course[0].numberGrade * course[0].creditValue) + (course[1].numberGrade *     course[1].creditValue)) / (course[0].creditValue + course[1].creditValue);
System.out.println(Courses.GPA);
}
}

(f.equalsIgnoreCase(Courses.letterGrade)) ----- is wrong.

• Replace Courses.letterGrade with Course[coursenum].lettergrade
• remove continue,no need of that .
• better design is to use switch statement.
• Courses is a Class not a object u cannot store in it. You have created a object of type Courses 'courses' in this u can store.
  replace Courses.Gpa to a integer variable.

I have found several issues in your code, besides the things already stated in the comments:

• Although you create an array of Courses, you never actually create any Courses objects, which you add to the array. When there are no Courses in your array, you also cannot assign your variables.
• You should use a Map to avoid having to use all of these ifs.
• The naming of your class is misleading. The array should be called courses and the class should be called Course.

I tried to rebuild your code so that it makes sense to me and works as I think it should.

import java.util.HashMap;
import java.util.Scanner;
class Course {
public String letterGrade;
public int numberGrade;
public int creditValue;
//public float GPA; // this should not be part of your Course class
Course(int credits, int gradeNum, String gradeLet) {
letterGrade = gradeLet;
numberGrade = gradeNum;
creditValue = credits;
}
}
public class GradeCruncher {
static Scanner userInput = new Scanner(System.in);
static HashMap<String, Integer> gradeMap = getGradeMap(); 
public static void main(String[] args) {
int numOfCourses;
int courseNum = 0;
System.out.println("How many courses would you like to input?");
numOfCourses = userInput.nextInt();
// create the array to store the courses
Course[] courses = new Course[numOfCourses];
// loop to get all courses
for (; courseNum < numOfCourses; courseNum++) {
System.out.println("Enter info for course " + courseNum);
System.out.println("How many credits is this course worth?");
// Get the credits for this course from input and save it temporarily
int tempCredits = userInput.nextInt();
System.out.println("Credits is " + tempCredits);
System.out.println("What is your current letter grade for this course?");
// this is needed so that the scanner removes the newline (\n) from the input
userInput.nextLine();
// Get the letter grade for this course from input and save it temporarily
String tempLetterGrade = userInput.nextLine();
System.out.println("Letter grade is " + tempLetterGrade);
// Retrieve the number grade from the map and save it
int tempNumberGrade = gradeMap.get(tempLetterGrade);
// Create the Course object with the input values and save it in the courses array
courses[courseNum] = new Course(tempCredits, tempNumberGrade, tempLetterGrade);
}
// All courses built
// Calculate GPA
double gpa = 0.0;
int overallCreditValue = 0;
for (int i = 0; i < courses.length; i++) {
gpa += (courses[i].numberGrade * courses[i].creditValue);
overallCreditValue += courses[i].creditValue;
}
gpa = gpa / overallCreditValue;
System.out.println("GPA Calculated: " + gpa);
}
private static HashMap<String, Integer> getGradeMap() {
HashMap<String, Integer> gradeMap = new HashMap<String, Integer>();
gradeMap.put("a+", 100);
gradeMap.put("a", 93);
gradeMap.put("a-", 90);
gradeMap.put("b+", 87);
gradeMap.put("b", 83);
gradeMap.put("b-", 80);
gradeMap.put("c+", 77);
gradeMap.put("c", 73);
gradeMap.put("c-", 70);
gradeMap.put("d+", 67);
gradeMap.put("d", 63);
gradeMap.put("d-", 60);
gradeMap.put("f", 0);
return gradeMap;
}
}

Explanation:

The letter and number grades are mapped in a map. The Course Class is now structured, so that the contents are input via the constructor. First all the inputs are retrieved from the user for each course and stored temporarily. When all the course info is retrieved, the Course object is created with this information and then stored in the courses array. When all courses are created, the average is calculated (according to the way you did it) and printed to the output.

Input and output:

How many courses would you like to input?
2
Enter info for course 0
How many credits is this course worth?
5
What is your current letter grade for this course?
a+
Enter info for course 1
How many credits is this course worth?
5
What is your current letter grade for this course?
a
GPA Calculated: 96.5