Array Operations

This is a discussion on Array Operations within the C Programming forums, part of the General Programming Boards category; Hello! I'm having a difficult time with this bit of code my value index is supposed to be set to ...

  1. #1
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    Array Operations

    Hello!
    I'm having a difficult time with this bit of code
    my value index is supposed to be set to the 'row' with the lowest value of "err"
    but index is never set to anything higher than 0. no matter my input
    'data' is 1 dimensional array taken from a file with 200 rows (numRows) and 6 columns (numCols) of data type double
    Code:
    void safeTest(double *testPoint, double *data, int numRows, int numCols)
    {
    	int r, c, i, index = 0;
    	double sum, err = 0;
    	double oper[numCols-1];
    	double temp = 1000000;
    
    
    	for(i = 0; i < numCols-1; i++)   
    	{
    		oper[i] = testPoint[i];
    	}
    
    	for(r = 0; r < numRows; r++)
    	{ 
    		for(c = 0; c < numCols; c++)
    		{
    			oper[c] -= data[r*numCols+c];
    			oper[c] =  oper[c] * oper[c];
    			sum     += oper[c];
    		}
    
    		err = sqrt(sum);
    		sum = 0;
    
    		for(i = 0; i < numCols-1; i++)
    		{
    			oper[i] = testPoint[i];
    		}
    
    		if(temp > err)
    		{
    			temp = err;
    			index  = r;
    		}
    
    	}
    
    
    	if(data[index*numCols + 5] == 1)
    	{
    		printf("It is SAFE to move on\n");
    	}else
    	{
    		printf("It is NOT SAFE to move on\n");
    	}
    }
    Thank you for any help!

  2. #2
    ATH0 quzah's Avatar
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    Code:
    double oper[numCols-1];
    ...
    for(c = 0; c < numCols; c++)
    You have a problem there.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Sorry I should have clarified that. That value doesn't include the last column of data so it is correct

  4. #4
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    Code:
    		for(c = 0; c < numCols; c++)
    		{
    			oper[c] -= data[r*numCols+c];
    			oper[c] =  oper[c] * oper[c];
    			sum     += oper[c];
    		}
    oper array max indice you can get safely is oper[numCols-2].
    Array with dimension N, valid indices [0-N-1].

  5. #5
    ATH0 quzah's Avatar
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    Quote Originally Posted by cswimmer View Post
    Sorry I should have clarified that. That value doesn't include the last column of data so it is correct
    That's not the problem I was talking about. Say numCols is 2. Then:
    Code:
    double oper[2-1]; /* 2 - 1 = 1 */
    ...
    for(c = 0; c < 2 /* loop for element 0 and element 1 */; c++)
       ... oops, oper[ 1 ] is out of bounds of your array
    Quzah.
    Hope is the first step on the road to disappointment.

  6. #6
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    Quote Originally Posted by Bayint Naung View Post
    oper array max indice you can get safely is oper[numCols-2].
    Array with dimension N, valid indices [0-N-1].
    Thanks Bayint I was able to fix it with this:
    Code:
    int safeTest(double *testPoint, double *data, int numRows, int numCols){
    	int r, c, i, index = 0;     
    	double sum, eucl = 0;       
    	double oper[numCols];       
    	double temp = 10000000.0;   
    	char advance[100] = "no";
    
        for(r = 0; r < numRows; r++){
            for(c = 0; c < numCols; c++){                                   
                oper[c] = data[r*(numCols+1)+c];                            
                sum += (oper[c] - testPoint[c])*(oper[c] - testPoint[c]);   
            }
                eucl = sqrt(sum);                                           
                sum = 0;                                                    
    
                if(temp > eucl){                                            
    
                    temp = eucl;                                            
                    index  = r;                                             
                }
        }
    	if(data[index*(numCols+1) + 5] == 1.0){                             
    
    	    printf("It is SAFE to move on\n");
    	}else{                                                              
            printf("It is NOT SAFE to move on\n");
    	 }

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