Have you tried a simpler, shorter, more easily debugged sketch?
case 'A': returnValue = A; break;
case 'a': returnValue = A; break;
case 'B': returnValue = B; break;
case 'b': returnValue = B; break;
case 'C': returnValue = C; break;
case 'c': returnValue = C; break;
case 'D': returnValue = D; break;
case 'd': returnValue = D; break;
case 'E': returnValue = E; break;
case 'e': returnValue = E; break;
case 'F': returnValue = F; break;
case 'f': returnValue = F; break;
case 'G': returnValue = G; break;
case 'g': returnValue = G; break;
case 'H': returnValue = H; break;
case 'h': returnValue = H; break;
case 'I': returnValue = I; break;
case 'i': returnValue = I; break;
case 'J': returnValue = J; break;
case 'j': returnValue = J; break;
case 'K': returnValue = K; break;
case 'k': returnValue = K; break;
case 'L': returnValue = L; break;
case 'l': returnValue = L; break;
case 'M': returnValue = M; break;
case 'm': returnValue = M; break;
case 'N': returnValue = N; break;
case 'n': returnValue = N; break;
case 'O': returnValue = O; break;
case 'o': returnValue = O; break;
case 'P': returnValue = P; break;
case 'p': returnValue = P; break;
case 'Q': returnValue = Q; break;
case 'q': returnValue = Q; break;
case 'R': returnValue = R; break;
case 'r': returnValue = R; break;
case 'S': returnValue = S; break;
case 's': returnValue = S; break;
case 'T': returnValue = T; break;
case 't': returnValue = T; break;
case 'U': returnValue = U; break;
case 'u': returnValue = U; break;
case 'V': returnValue = V; break;
case 'v': returnValue = V; break;
case 'W': returnValue = W; break;
case 'w': returnValue = W; break;
case 'X': returnValue = X; break;
case 'x': returnValue = X; break;
case 'Y': returnValue = Y; break;
case 'y': returnValue = Y; break;
case 'Z': returnValue = Z; break;
case 'z': returnValue = Z; break;
or
if ((charachter >= 'a' && charachter <='z') ||
(charachter >= 'A' && charachter <='Z'))
{
returnValue = toupper (charachter) - 'A';
}
const int powers[] = {1,2,4,8,16,32,64,128};
Wuh?