invalid syntax at '=' . A '(' might be missing a closing ')'

The error is at line 14 and 26

switch nargin
    case 0
        disp('Non ci sono stati input per la funzione!')
    case 1
        if (f = 0)
        disp('Non hai inserito correttamente la funzione la funzione')
        end
    case 2
        if(~isscalar(xo) || isinteger(xo))
        disp('Mammt')
        end
    case 3
        if(~isscalar(xo) || isinteger(xo)) % anche se ci sta un altro controllo che nello non vuole dirmi
        disp('A')
        end
    case 4
        if(~isinteger(NMAX) || NMAX = 0 || ischar(NMAX))
        disp('A pecrrrr, cioè nmax non va bene')
        end
end

Answer 1

[Catalytic]

if (f == 0)

and same thing in this line

      if(~isinteger(NMAX) || NMAX == 0 || ischar(NMAX))

[Guillaume]

Note that matlab is not C, there is no need to enclose a conditional statement in (), so

if f == 0
    
if ~isinteger(NMAX)  || NMAX == 0 || ischar(NMAX)

Note that isinteger check that the type is integer not that the values are integer,

>> isinteger(1)   %return false, since double is not an integer type
ans =
  logical
   0
>> isinteger(uint8(1))  %return true, the type is integer
ans =
  logical
   1

I suspect that you meant to test if the value was integer, not the type.

Also note that the ischar(NMAX) is redundant, if NMAX is char, it will have failed the ~isinteger test.

You may want to use validateattributes instead of writing your own tests:

validateattributes(f, {'numeric'}, {'nonzero', 'scalar'});

validateattributes(NMAX, {'numeric'}, {'integer', 'nonzero', 'scalar'})