Using for loop to access two elements from array

I am trying to convert an array of bit values into complex values. For every two elements the first is designated as the real part and the second as the imaginary part. I am confused how to access the current index and the next index without exceeding the number of array elements.

str='abc';
str_dec=double(str); %converts to decimal
str_bin=dec2bin(str_dec,8) %converts string from decimal to binary
bits=reshape(str_bin.',1,8*length(str))
QPSK = [];

%grab every two elements from bits to convert to QPSK
for i = length(bits)
    %convert bits to complex values
    if bits(i) > 1
        if bits(i+1) > 1
            QPSK = [QPSK, 1+1j];
        else
            QPSK = [QPSK, 1-1j];
        end
    else
        if bits(i+1) > 1
            QPSK = [QPSK, -1+1j];
        else
            QPSK = [QPSK, -1-1j];
        end
    end 
end
QPSK

Answer 1

[Matt J]

Forget the loop. It's a four-line operation:

str='abc';

bits=reshape( dec2bin(str,8).' ,1,[]) -'0'; %converts string from decimal to binary

parts=2*bits-1;

QPSK=complex( parts(1:2:end) ,  parts(2:2:end) )

QPSK = 
  -1.0000 + 1.0000i   1.0000 - 1.0000i  -1.0000 - 1.0000i  -1.0000 + 1.0000i  -1.0000 + 1.0000i   1.0000 - 1.0000i  -1.0000 - 1.0000i   1.0000 - 1.0000i  -1.0000 + 1.0000i   1.0000 - 1.0000i  -1.0000 - 1.0000i   1.0000 + 1.0000i