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];

Declare it then.

Code:

int residue[50];