Converting hexadecimal to decimal in base 10 using a loop (not function hex2dec)

I am running the following code and it is only working when I plug in either just numbers or just letters, but I cannot get it to work for both. For example, "F4E" will not work, but "FF" or "44" work. Why is this happening?

num = input('Enter a hexidecimal number (e.g. FF):', 's');

y = double(num);
x = 0;

for i = 1:length(num)
    
    if y > 47 & y < 58
        y = y - 48;
    elseif y > 64 & y < 71
        y = y - 55;
    elseif y > 96 & y < 103
        y = y - 87;
    end
  
    x = x + y(i) * 16^(length(num)-i);
  
end

Answer 1

[Walter Roberson]

if y > 47 & y < 58

should be indexing y(i)

Answer 2

[Guillaume]

For reference, here is how I would implement the conversion efficiently in matlab (without using hex2dec):

hex = upper(input('Enter a hexidecimal number (e.g. FF):', 's'));
lookup = [];
lookup(['0':'9', 'A':'F']) = 0:15;  %lookup table to convert character to corresponding decimal value
dec = polyval(lookup(hex), 16);   %convert characters to decimal value and multiply by corresponding power of 16

No loop needed.

Answer 3

[vamsi krishna]

a=input("enter the no. in double quotes ");

A=char(a);

l=strlength(a);

i=1;b=0;

while (l>0)

if ((A(i)>='0')&&(A(i)<='9'))

b=(A(i)-48)+b*16;

elseif ((A(i)>='A')&&(A(i)<='E'))

b=(A(i)-55)+b*16;

end

i=i+1;

l=l-1;

end

fprintf("value of given no. %s in decimal is %d",a,b);