Display a message only one time in a recursion containing a for loop

Consider this simple code

a=[1 1 0 1];
recursion(a)

with

function a=recursion(a)
    if isempty(a)
        disp('a does not contain 0')
    else
         for i=1:numel(a)
            if a(1)==0
                disp('a contains 0')
                return
            end
            a=a(2:end);
            recursion(a);
         end
    end
end

Don't focus on the aim of the code (of course the job could be done in 1 line or 2) but on the output

a contains 0
a contains 0
a contains 0
a contains 0

ans =

       0     1

Is it possibile to output the message "a contains 0" only one time AND then to output the modified vector "a" ? i.e. is it possibile to have this output

a contains 0

ans =

       0     1

Answer 1

[Walter Roberson]

Do not have recursion return a, since the changed value is not used. Instead, have it return a status as to whether it encountered a 0. Check the output and if set then break out the the loop and return 1. Only return 0 if you get to the end of the loop without a 0.

[giannit]

Thanks for the answer, you mean this?

a=[1 1 0 1];
found=recursion(a);
if found
    disp('a contains 0')
else
    disp('a doesn''t contain 0')
end

with

function found=recursion(a)
    if isempty(a)
        found=0;
    else
         for i=1:numel(a)
            if a(1)==0
                found=1;
                return
            end
            a=a(2:end);
            found=recursion(a);
         end
    end
end

[Walter Roberson]

Change

found=recursion(a);

to

if recusion(a)
   found = 1;
   break;
end

[giannit]

Sorry I don't understand, in that way the output argument will not be assigned, right?

Using:

find=recursion(a);
if find
    disp('a contains 0')
else
    disp('a don''t contain 0')
end

function found=recursion(a)
    if isempty(a)
        found=0;
    else
         for i=1:numel(a)
            if a(1)==0
                found=1;
                return
            end
            a=a(2:end);
            if recursion(a)
               found = 1;
               break;
            end
         end
    end
end

with a=[1 1 0 1] it prints

a contains 0

but whit a=[1 1 1 1] it says

Output argument "found" (and maybe
others) not assigned during call to
"recursion".

EDIT

maybe this one is even better

a=[1 1 0 1];
found=recursion(a,0);
if found
    disp('a contains 0')
else
    disp('a don''t contain 0')
end

with

function found=recursion(a,found)
    for i=1:numel(a)
        found=a(1)==0;
        if found
            return
        end
        a=a(2:end);
        recursion(a);
    end
end

[Walter Roberson]

function found=recursion(a,found)
    for i=1:numel(a)
        found=a(1)==0;
        if found
            return
        end
        a=a(2:end);
        found = recursion(a);
        if found; break; end
    end
end

[giannit]

Ok many thanks, why you put another if after the recursion call? Moreover, should I also change "return" with "break" in the first if ?

[Walter Roberson]

The "break" could be changed to return. The idea is that as soon as you see it found you do not need to examine the rest of a in the for loop.