Hi,
I have wrote a program to do multiple linear regression (form the matrix ) and solve the relevant matrix using Gaussian Elimination,Unfortunately it is not running and once I get it to run it is gives me the error stating det=0.
Please have a look and let me know how to fix it.

// Multiple Linear Regression

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


//#define limit 10
//#define Max  20   


 //void main()

//{
    int i;                        //Loop counter
    int N;                         //Number of data points
    double X1[Max];               //X1 values presented by matrix elements 
    double X2[Max];               //X2 values presented by matrix elements
    double Y[Max];               //Y values presented by matrix elements
    double SumX1;                  //sum Value of X1
    double SumX2;                  //Sum Value of X2 
    double SumX1X1;                 //Sum Value of X1*X1
    double SumX1X2;                 //Sum Value of X1*X2
    double SumX2X2;                 //Sum Value of X2*X2
    double SumY;                  //sum Value Y
    double SumX1Y;                 //Sum Value of Y*X1
    double SumX2Y;                 //Sum Value of Y*X2
    int K, P, C, J;                  //Loop Counters
    double M[3][4];                  //Gaussian Input
   
    int    Row[Max];                 //Pointer Vector
    double a[Max];                   //Unknown Vector
    double SUM, Z;                                                       
    int  Pivot;

   

   // printf("Enter Number of Data points,It should be less than %d :\n",Max);
   // scanf_s("%d",&N);
        
   // for(i = 1; i <= N; i++)
    //{
        printf("For Data Point Number %d ,Enter values of X1,X2 and Y seperated by comma.\n",i);
        scanf_s("%lf,%1f,%1f", &X1[i-1],&X2[i-1],&Y[i-1]);
    }
	//Calculating Sum X1
   // SumX1 = 0.0;     //Setting the initial value
    
    //for(i = 1; i <= N; i++) SumX1 = SumX1 + (X1[i-1]);

	//Calculating Sum X2

    //SumX2 = 0.0;    //Setting the initial value
    //for(i = 1; i <= N; i++) SumX2 = SumX2 + (X2[i-1]) ;

	//Calculating SumY

    //SumY = 0.0;   // Setting the initial Value
    //for(i = 1; i <= N; i++) SumY = SumY + (Y[i-1]);

	//Calculating SumX1^2

    //SumX1X1 = 0.0; //Setting the initial Value
   // for(i = 1; i <= N; i++) SumX1X1 = SumX1X1 +( (X1[i-1] ) * (X1[i-1] ) );

	//Calculating SumX2^2

    //SumX2X2 = 0.0; //Setting the initial Value
    //for(i = 1; i <= N; i++) SumX2X2 = SumX2X2 +( (X2[i-1] ) * (X2[i-1] ) );

	//Calculating SumX1.X2

    //SumX1X2 = 0.0; //Setting the initial Value
    //for(i = 1; i <= N; i++) SumX1X2 = SumX1X2 +( (X1[i-1] ) * (X2[i-1] ) );

	//Calculating SumX2.Y

    //SumX1Y = 0.0; //Setting the initial Value
   // for(i = 1; i <= N; i++) SumX1Y = SumX1Y +( (X1[i-1] ) * (Y[i-1] ) );

	//Calculating SumX1.Y

    //SumX2Y = 0.0; //Setting the initial Value
   // for(i = 1; i <= N; i++) SumX2Y = SumX2Y +( (X2[i-1] ) * (Y[i-1] ) );

	//Forming the Gaussian Input Matrix

	//M[0][0] = N;
	//M[0][1] = SumX1;
	//M[0][2] = SumX2;
	//M[0][3] = SumY;
	//M[1][0] = SumX1;
	//M[1][1] = SumX1X1;
	//M[1][2] = SumX1X2;
	//M[1][3] = SumX1Y;
	//M[2][0] = SumX2;
	//M[2][1] = SumX1X2;
	//M[2][2] = SumX2X2;
	//M[2][3] = SumX2Y;

       //Forming Pointer Vector
	   //for (J = 1; J<= 3; J++) Row[J-1] = J - 1;

       //Upper Triangular Matrix

       //for (P = 1; P <= 2; P++)
       {

       //Pivoting

      //for (K = P + 1; K <= 3; K++)
      {
        if ( fabs(M[Row[K-1]][P-1]) > fabs(M[Row[P-1]][P-1]) )
        {

           Pivot      = Row[P-1];
           Row[P-1] = Row[K-1];
           Row[K-1] = Pivot;
        }
      } 



     //for (K = P + 1; K <= 3; K++)
     { 
       Z = M[Row[K-1]][P-1] / M[Row[P-1]][P-1];

   
       //for (C = P + 1; C <= 4; C++)
       {
          M[Row[K-1]][C-1] -= Z * M[Row[P-1]][C-1];
       }
     } 

  } 

   // if( M[Row[2]][2] == 0)
    {
    //  printf("Matrix determinant is Zero,Failure to apply Gaussian Elimination Method !\n");
      exit(1);
    }

    // Back substitution    
    //a[2] = M[Row[2]][3] / M[Row[2]][2];

   // for (K = 2; K >= 1; K--)
    {
      SUM = 0;
      for (C = K + 1; C <= 3; C++)
      {
           SUM += M[Row[K-1]][C-1] * a[C-1];   
      }

      a[K-1] = ( M[Row[K-1]][3] - SUM) / M[Row[K-1]][K-1];

    }  // End of back substitution 

    
	//for( K = 1; K <= 3; K++)  printf("Final answer for a[%d] = %lf\n", K, a[K-1]); 
 }

You're going to have to write out the error messages because most people don't know the error codes off the top of their heads.