Why do I get a for loop error "Subscript indices must either be real positive integers or logicals"?

I have the following code (below) that uses a for loop. Why do I get the error "Subscript indices must either be real positive integers or logicals"?

data.Year=year(data.Date);
data.Month=month(data.Date);
data.Day=day(data.Date);
data.Hour=hour(data.Date)+1;
data.Wday=weekday(data.Date);
data.Bday=isbusday(data.Date);
data.Hday=1*((data.Bday==0)&((data.Wday~=1)&(data.Wday~=7)));
data.Hday2=data.Hday;
[rows, cols]=size(data.Hday);
for m=1:rows
    if (data.Hday(m)==1)&&((data.Month(m)==12)||(data.Month(m)==11)||(data.Month(m)==9)|(data.Month(m)==7)|(data.Month(m)==5))
        data.Hday2(m)=data.Hday(m)+1;
        data.nday(m)=0;
    elseif (data.Hday(m)==1)&&(data.Month(m)==1)&&(data.Day(m)<8)
        data.Hday2(m)=data.Hday(m)+1;
        data.nday(m)=0;
    elseif (data.Hday(m)==1)
        data.Hday2(m)=1;
        data.nday(m)=0;
    elseif (data.Hday(m-1)==1)&&(data.Month(m-1)==11)
        data.Hday2(m)=.5
    else
        data.Hday2(m)=0;
        data.nday(m)=1;
    end
end

Answer 1

[Geoff Hayes]

The problem is because of m

 for m=1:rows

Note how m starts at 1. Now look at this line

elseif (data.Hday(m-1)==1)&&(data.Month(m-1)==11)

You are subtracting 1 from m and so when m is one, then m-1 is zero which is not a real positive integer. MATLAB arrays are one-based and so the minimum index into an array is one.