Thread: Little Problem

This little bit of code is meant to scan each row of "array" noting the position of the element with the maximum value in each row and writing that position in to "maxArray" but it doesnt appear to be working. Any suggestions as to why this isnt working? Thanks

Code:

  for(i=0; i<4; i++)
     {
        for(j=0; j<4; j++)
         {
          if(array[j][i] > XMax)
          XMax = j;
         }
         maxArray[i] = XMax;
     }

That was one problem...the other problem was this:

XMax = j;

This was setting the MAX to what J was....you are using j for the loop counter...you want the MAX to be the VALUE of j, then store the position of j...but the j and i were backwards too...this code is correct and working to fix both problems:

Code:

for(i=0; i<4; i++)
     {
        for(j=0; j<4; j++)
         {
			if(array[i][j]>XMax)
			{
				XMax=array[i][j];
				maxArray[i]=j;
			}
         }
	}

enjoy.

Thanks for that, it all seems fine now. The indexes being the wrong way round was just me being sloppy when I was typing this out. Deliberate mistake and all that.............

Thanks a lot!

Back again! This is a little expansion of the problem above so why waste space with a new topic. The code was sorted and working well but when I expanded it to scan a 64x64 array it gets the position of the first 4 or 5 maximum elements then just repeats the next one for the next 59 or so elements of maxArray. Seems like its bailing out or something. Any suggestions?

Code:

#include <stdio.h>
#include <stdlib.h>

int main(){

int i=0, j=0;
int array[64][64], maxArray[64];
int XMax=0;
char filename[20];
FILE *fHandle;

printf("Enter Filename: ");
scanf("%s", filename);

if((fHandle = fopen(filename, "r")) == NULL)
{
		printf("Unable to open file");
  return 0;

}
else
{

for(i=0; i<64; i++)
		{
			for(j=0; j<64; j++)
			{
				fscanf(fHandle, "%d", &array[i][j]);
			}
		}

}

for(i=0; i<64; i++)
     {
        for(j=0; j<64; j++)
         {
			if(array[i][j]>XMax)
			{
				XMax=array[i][j];
				maxArray[i]=j;
			}
         }
     }
}

As I said before it works for a 4x4 array but doesnt work for a 64x64 array. Confused!

weird...i'm in a hurry now so I don't really have time to mess with it...but off the top of my head I would *guess* that when the characters are being read in, something funny is going on.....since the code for the 4x4 worked, it's not going to fail on the 64x64...and I couldn't see any prominent typos...So I would toy around with the way the characters are being read in.....I couldn't think of anything else at the time..........don't forget to close your file, too......

Ive messed about a bit but still no luck. The first 5 elements of maxArray are always correct but then the 6th one is 0 then it gets the 7th, 8th, 9th and 10th correct but then returns 0 up to the 16th element which is correct. Its pretty eratic like this all the way up to the 64th element with a lot of 0's which I know shouldnt be there!

The file does get closed aswell now by the way!

> int i=0, j=0;
> int array[64][64], maxArray[64];
> int XMax=0;
> char filename[20];
> FILE *fHandle;
Depending on your compiler, this is over 8K (or 16K) of local variables.

Some old (ie DOS) compilers only allocate a few K of stack.

Try moving the arrays off the stack like so
static int array[64][64], maxArray[64];

that didnt work. Its a windows based compiler (Dev C++ 4). Pretty up to date. Ive noticed aswell now that it doesnt always work for the 4 by 4 array. It sommetimes messes up the 4th element. First 3 are always correct though. sheer baffledness has come over me.

In that case, check your input

Code:

if ( fscanf(fHandle, "%d", &array[i][j]) != 1 ) {
    printf( "Error reading file at i=%d, j=%d\n", i, j );
}

Theres no errors in the input. Ive tried a few different txt files and a couple of dat files and the patern in the output is the same for each one (with the first 6 elements fine and eratic 0's.....).

The source code and input should be attached below! The input txt file has been set up so that the output array should read 0 to 63. Its decided to change its mind today and only get the first 3 elements and the 19th correct?? Im hoping ive just been a complete idiot here and missed something simple.

You orginally asked
> This little bit of code is meant to scan each row of "array" noting the position of the element with the maximum value in each row and writing that position in to "maxArray"

If you're expecting this from your example data
0
1
2
3
4
5
6
7
8
9
etc


Then you need to change your code as follows

Code:

    for(row=0; row<64; row++)
    {
        XMax = 0;               // new row, new max
        for(col=0; col<64; col++)
        {
            if(array[row][col]>XMax)
            {
                XMax=array[row][col];
                maxArray[row]=col;
            }
        }
    }