arrays and pointers

This is a discussion on arrays and pointers within the C Programming forums, part of the General Programming Boards category; does anyone know what is wrong with this? Code: int iteration; int i,j; double sum; for (iteration=0;iteration<20;iteration++) { /*x1[i] =1/a[i][i] ...

  1. #1
    Registered User
    Join Date
    Jan 2009
    Posts
    8

    arrays and pointers

    does anyone know what is wrong with this?

    Code:
            int iteration;
            int i,j;
            double sum;
    
            for (iteration=0;iteration<20;iteration++)
            {
                    /*x1[i] =1/a[i][i] *(b[i] -(sum on j, except j=i)a[i][j]*x0[j])
                            for i=0,...,4. (2b)*/
                    for (i=0;i<=4;i++)
                    {
                            sum=0;
                            for (j=0;j<=4;j++)
                                    if (i!=j)
                                            sum+=a[i][j]*x0[j];
                            x1[i]=1.0/a[i][i]*(b[i]-sum);
                    }
                    printf("Iteration %d:\n",iteration);
                    for (i=0;i<=4;i++)
                            printf("%15.4e ",x1[i]);
                    printf("\n");
                    //copy x1 to x- for the next iteration
                    memcpy(x0,x1,4*sizeof(double));
            }
    
            //compute and display residue
            for (i=0;i<=4;i++)
                    residue[i]=b[i]-a[i][i]*x1[i];
            printf("Residue:\n");
            for (i=0;i<=4;i++)
                    printf("%12.4e ",residue[i]);
    
            return;
    }
    when i compile, i get the error:

    `residue' undeclared (first use in this function)
    (Each undeclared identifier is reported only once
    for each function it appears in.)

    the line they are talking about is:

    residue[i]=b[i]-a[i][i]*x1[i];
    Last edited by flamehead144; 03-05-2009 at 11:06 AM.

  2. #2
    Registered User
    Join Date
    Sep 2008
    Posts
    58
    Declare it then.

    Code:
    int residue[50];

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