Java - 最高，最低和最低

Question

I've just started studying and I need help on one of my exercises.

I need the end user to input a rain fall number for each month. I then need to out put the average rainfall, highest month and lowest month and the months which rainfall was above average.

I keep getting the same number in the highest and lowest and I have no idea why. I am seriously pulling my hair out. Any help would be greatly appreciated.

This is what I have so far:

public class rainfall {

    /**
     * @param args
     */
    public static void main(String[] args) 
    {
    int[]  numgroup;
    numgroup = new int [13];
    ConsoleReader console = new ConsoleReader();
    int highest;
    int lowest;
    int index;
    int tempVal;
    int minMonth;
    int minIndex;
    int maxMonth;
    int maxIndex;


    System.out.println("Welcome to Rainfall");

    for(index = 1; index < 13; index = index + 1)
    {       
        System.out.println("Please enter the rainfall for month " + index);
                tempVal = console.readInt();
                while (tempVal>100 || tempVal<0)
                    {
                    System.out.println("The rating must be within 0...100. Try again");
                    tempVal = console.readInt();
                    }
                numgroup[index] = tempVal;
    }           



    lowest = numgroup[0];


        for(minIndex = 0; minIndex < numgroup.length; minIndex = minIndex + 1);
        {
                if (numgroup[0] < lowest)
                {
                lowest = numgroup[0];
                minMonth = minIndex;
                }
        }

    highest = numgroup[1];


            for(maxIndex = 0; maxIndex < numgroup.length; maxIndex = maxIndex + 1);
            {
                    if (numgroup[1] > highest)
                    {
                    highest = numgroup[1];
                    maxMonth = maxIndex;
                    }
            }


        System.out.println("The average monthly rainfall was ");
        System.out.println("The lowest monthly rainfall was month " + minIndex);
        System.out.println("The highest monthly rainfall was month " + maxIndex);

        System.out.println("Thank you for using Rainfall");

    }


    private static ConsoleReader ConsoleReader() {

        return null;
    }

}

Thanks,

Emily

Answer 1

First, since this is your homework, you should not be asking it on stackoverflow.com

Now let have a look at your code

1. lowest = numgroup[0];

Why? It seems that you trying to use this algorithm to find min:

1.1 Suppose first number (which you think is numgroup[0] ) is min (named as lowest in your code)
1.2. Compare it with all other numbers, if any of the numbers is smaller, replace min (ie lowest ).

But, numgroup[0] is not your first number! You started your first for loop like this

for(index = 1;...

So, your first number is numgroup[1] .

Next, your second loop starts like

for(minIndex = 0;

whereas the element at index 0 is never even intended to be used by you (I guess)

Next, your condition for finding out if the number in current iteration is less than lowest is

if (numgroup[0] < lowest)

which always compares element at index 0 with lowest which (I guess) is not your intention.

Answer 2

instead of

if (numgroup[0] < lowest)

you have to write

if (numgroup[minIndex] < lowest)

the same goes for

if (numgroup[1] > highest)

which should be

if (numgroup[maxIndex] > highest)

Answer 3

You do

lowest = numgroup[0]

and then

if (numgroup[0] < lowest)

which will never be "true" as numgroup[0] is always equal to lowest. Rather your if-clause should be something like if (numgroup[minIndex] < lowest) . The same thing applies for highest.

Answer 4

public static void main(String[] args) 
{
int[] numgroup = new int [12]; // 12 months - 12 elements
ConsoleReader console = new ConsoleReader();
int highest;
int lowest;
int index;
int tempVal;
int minIndex;
int maxIndex;


System.out.println("Welcome to Rainfall");
// Input (index now 0-based)
for(index = 0; index < 12; index = index + 1)
{       
    System.out.println("Please enter the rainfall for month " + index + 1);
    tempVal = console.readInt();
    while (tempVal>100 || tempVal<0)
    {
        System.out.println("The rating must be within 0...100. Try again");
        tempVal = console.readInt();
    }
    numgroup[index] = tempVal;
}           

lowest = numgroup[0];
highest = numgroup[0];
int total = 0.0;
// Loop over data (using 1 loop)
for(index = 0; index < 12; index = index + 1)
{       
    int curr = numgroup[index];
    if (curr < lowest) {
        lowest = curr;
        minIndex = index;
    }
    if (curr > highest) {
        highest = curr;
        maxIndex = index;
    }
     total += curr;
}
float avg = (float)total / numgroup.length;

System.out.println("The average monthly rainfall was " + agv);
// +1 to go from 0-based index to 1-based month
System.out.println("The lowest monthly rainfall was month " + minIndex + 1);
System.out.println("The highest monthly rainfall was month " + maxIndex + 1);

System.out.println("Thank you for using Rainfall");

}

Answer 5

Just try to use collections for min/max if there is no restriction in your homework.

Vector<Integer> rainfallData = new Vector<Integer>();
int avg = 0;

for(index = 1; index < 13; index = index + 1)
{       
    System.out.println("Please enter the rainfall for month " + index);
    tempVal = console.readInt();
    while (tempVal>100 || tempVal<0)
    {
        System.out.println("The rating must be within 0...100. Try again");
        tempVal = console.readInt();
    }
   rainfallData.add(tempVal);
   avg+=tempVal; 
}

avg /= rainfallData.size();
int min = Collections.min(rainfallData);
int max = Collections.max(rainfallData);

Otherwise a min/max should look like this:

public int min(int[] vals) {
    if( vals==null || vals.length==0} {
           throw new IllegalArgumentException();
    } else if( vals.length == 1 ) {
         return vals[0];
    }
    int min = vals[0]; // Dont initialize with Integer.MAX_VALUE or so
    for(int i = 1; i < vals.length; ++i ) {
        if( vals[i] < min ) {
           min = vals[i];
        }
    } 
    return min;
}

Answer 6

for (index = 0; index < 12; index++) {

}

change the first for loop and the following

lowest = numgroup[0];

for (minIndex = 0; minIndex < numgroup.length; minIndex = minIndex + 1)
{
    if (numgroup[minIndex] < lowest) {
        lowest = numgroup[minIndex];
    }
}

highest = numgroup[0];

for (maxIndex = 0; maxIndex < numgroup.length; maxIndex = maxIndex + 1)
{
    if (numgroup[maxIndex] > highest) {
         highest = numgroup[maxIndex];
     }
}