What is wrong with the code?

I am trying to find the logest subsequence of 1s in a string. I am doing something wrong.

s='0101010111000101110001011100010100001110110100000000110001001000001110001000111010101001101100001111'
c=[]
counter = 0
for i = 2:length(s)
while str2num(s(i)) == 1 && str2num(s(i)) == str2num(s(i-1))
counter = counter+1
c = [c,counter]
if str2num(s(i)) ==0
counter = 0
end
end
end

[Walter Roberson]

hint: instead of doing str2num() and comparing to 1, you can just compare s(i) == '1', and you can compare s(i) == s(i-1)

[GEORGIOS BEKAS]

does not work

Answer 1

[Birdman]

Use regexp.

regexp(s,'1*','match')

and you will find that the longest subsequence consists of 4 elements.

[GEORGIOS BEKAS]

if isempty(y) == 1 y = 0 else y=length(y{max(length(y))} ) end

Answer 2

[Walter Roberson]

You have

counter = 0;
for i = 2:length(s)
while str2num(s(i)) == 1 && str2num(s(i)) == str2num(s(i-1))
counter = counter+1
c = [c,counter]
if str2num(s(i)) ==0
counter = 0
end
end

Trace it through.

Start with i = 2.

s(2) == 1 but s(1) is not 1, so end the while.

Go on to i = 3. s(3) == 0, so end the while.

Go on to i = 4. s(4) == 1, but s(3) is not 1, so end the while.

Go on to i = 5.... etc. You keep ending the while immediately until...

i = 9. s(9) == 1 and s(9) and s(8) are both 1, so enter the while loop.

Inside the while loop, increment counter to 1 and adjust c. s(9) is still not 0 so do not reset counter to 0. Continue around in the while loop.

i is still 9. s(9) and s(8) are still both 1, so enter the while loop. Inside the while loop, increment counter to 2 and adjust c. s(9) is still not 0, so do not reset counter to 0. Continue in the while loop.

i is still 9. s(9) and s(8) are still both 1, so enter the while loop. Inside the while loop, increment counter to 3 and adjust c. s(9) is still not 0, so do not reset counter to 0. Continue in the while loop.

...

ummm... when do we end the while loop? The while loop tests s(i) and s(i-1) but does not change either location and does not change i, so once entered, the while loop will never end.

[GEORGIOS BEKAS]

does not work

[Walter Roberson]

What did you change your code to?