Thread: Trying to write a program that reads from StdIn and findes the highest value

Hi!
I'm trying to write a program that counts the highest value in a matrix .
It does'nt work. What is wrong with it? If I put System.out print at bottom of main all hell breaks loose.
So...here it is:

public class 
{
	public static void main(String[] args) {
	//public static double[] [] readDouble2D()
 
			int M = StdIn.readInt();
			int N = StdIn.readInt();
			double[] [] a = new double [M] [N];
			for (int i = 0; i<M;i++)
				for (int j = 0; j < N;j++)
					a[i][j] = StdIn.readDouble();
				return a;
 
		}
	public static double max(double[] a)
		{
			double max = Double.NEGATIVE_INFINITY;
			for(int i = 0; i < a.length;i++)
				if (a[i] > max) max = a[i];
			return max;
		}
}

return a;
^
1 error

 
public class p151 {
  public static void main(String[] args) {
 
 
    int max = Integer.MAX_VALUE;
 
    while (!StdIn.isEmpty()) {
      int N = StdIn.readInt();
      if (N > max) {
        max = N;
    }
    System.out.println( max);
  }
}

I can't use this because it only finds the highest number in an array.It does'nt count them.

The error message is quite helpful. No 'void' method can have a return statement. Why is the return statement in your void main() method? What are you trying to do?

My program is supposed to read a file and return the number of highest value in the terrain, count the peaks so to speak.

My problem is the scope and print out.

Specifically, is the "return a;" statement in main() required? I suspect not, especially since it's not allowed in a void method which main() must be.

To print the value returned by your method max(), do something like:

double maxValue = max( a );
System.out.println( "The max is: " + maxValue );

The 2 lines of code could be condensed to one, but I wanted to show the detail so you might understand it better.

When I put the print statement in main and the second error message in static.

This is my problem a have got the concept, almost(hahah), my problem is the scope and chooing the right method and statements.

C:\P1529.java
1529.java:12: error: cannot return a value from method whose
 result type is void
                                return a;
                                       ^
P1529.java:21: error: cannot find symbol
                        System.out.println("The max is: " + MaxValue);
                                                            ^
  symbol:   variable MaxValue
 
2 errors
 
C:\>javac P529.java
1529.java:13: error: method max in class  cannot be applied to given types;
                                double maxValue=max(a);
                                                ^
  required: double[]
  found: double[][]
  reason: actual argument double[][] cannot be converted to double[] by method i
nvocation conversion
isthispossibleidoubt1529.java:14: error: cannot find symbol
                        System.out.println("The max is: " + MaxValue);
                                                            ^
  symbol:   variable MaxValue
  location: class 1529
2 errors
[COLOR="Silver"]

--- Update ---

This is the sad version that I got now.

public class 
{
	public static void main(String[] args) {
	//public static double[] [] readDouble2D()
 
			int M = StdIn.readInt();
			int N = StdIn.readInt();
			double[] [] a = new double [M] [N];
			for (int i = 0; i<M;i++)
				for (int j = 0; j < N;j++)
					a[i][j] = StdIn.readDouble();
				//return a;
				double maxValue=max(a);
			System.out.println("The max is: " + maxValue);
		}
	public static double max(double[] [] a)
		{
			double max = Double.NEGATIVE_INFINITY;
			for(int i = 0; i < a.length;i++)
				for(int j=0;j<N;j++)
				if (a[i] [i] > max) max = a[i] [i];
			return max;
		}
}

When I pipe in #4 I get:

The max is:1.0

Update:
I think I should have it like this at the end: if (a[i]>max)

Check this out.

What is wrong?

public class
{
	//Finding the max and counting them
	public static double max(double[] a, int lo, int hi) {
        if (lo < 0 || hi >= a.length || lo > hi)
            throw new RuntimeException("Subarray indices out of bounds");
        double max = Double.NEGATIVE_INFINITY;
        for (int i = lo; i <= hi; i++) {
            if (a[i] > max)
			{
			max = a[i];
			MaxCounter++;
			}
        }
        return max;
    }
 
	public static void main (String[] args)
 
	//(double[][] readDouble2D())
	{
	//Reading the array
		int M = StdIn.readInt();
		int N = StdIn.readInt();
		int MaxCounter=0;
		double[][] a = new double[M] [N];
		for (int i = 0; i < M; i++)
			for (int j = 0; j < N; j++)
				a[i][j] = StdIn.readDouble();
				int maxValue = max(a);
 
				StdOut.println(MaxCounter);
	}
}

Erorr:

2.java:31: error: method max in class 2 cannot be applied to given types;
int maxValue = max(a);
^
required: double[],int,int
found: double[][]
reason: actual and formal argument lists differ in length
1 error

What about that error message don't you understand? I realize they can be a bit cryptic (sometimes), especially if you haven't taken the time to READ them and apply them to your code and the error about which they complain. Let's break it down:

Omg2.java:31: error: method max in class Omg2 cannot be applied to given types;
int maxValue = max(a);

"31: method max cannot be applied to give types" - that means at line 31 the method max has been called with incorrect parameters.

The next line points to the offending statement (The caret, '^', actually points to the occurrence of the error if the formatting is preserved.)

"required: double[],int,int
found: double[][]"

The first line indicates the parameters required by the method max().
The second line indicates the parameter(s) found in the offending call. Since the parameter(s) found don't match the parameters required, there's an error.

Solution: Modify the code, either the method signature or the method call, so that the parameters match.