incremental search method script errors - octave

Question

I wrote my very first octave script which is a code for the incremental search method for root finding but I encountered numerous errors that I found hard to understand.
The following is the script:
clear
syms x;
fct=input('enter your function in standard form: ');
f=str2func(fct); % This built in octave function creates functions from strings
Xmax=input('X maximum= ');
Xinit=input('X initial= ');
dx=input('dx= ');
epsi=input('epsi= ');
N=10; % the amount by which dx is decreased in case a root was found.
while (x<=Xmax)
f1=f(Xinit);
x=x+dx
f2=f(x);
if (abs(f2)>(1/epsi))
disp('The function approches infinity at ', num2str(x));
x=x+epsi;
else
if ((f2*f1)>0)
x=x+dx;
elseif ((f2*f1)==0)
disp('a root at ', num2str );
x=x+epsi;
else
if (dx < epsi)
disp('a root at ', num2str);
x=x+epsi;
else
x=x-dx;
dx=dx/N;
x=x+dx;
end
end
end
end
when running it the following errors showed up:
>> Incremental
enter your function in standard form: 1+(5.25*x)-(sec(sqrt(0.68*x)))
warning: passing floating-point values to sym is dangerous, see "help sym"
warning: called from
double_to_sym_heuristic at line 50 column 7
sym at line 379 column 13
mtimes at line 63 column 5
Incremental at line 3 column 4
warning: passing floating-point values to sym is dangerous, see "help sym"
warning: called from
double_to_sym_heuristic at line 50 column 7
sym at line 379 column 13
mtimes at line 63 column 5
Incremental at line 3 column 4
error: wrong type argument 'class'
error: str2func: FCN_NAME must be a string
error: called from
Incremental at line 4 column 2
Below is the flowchart of the incremental search method:

Answer 1

The problem happens in this line:
fct=input('enter your function in standard form: ');
Here input takes the user input and evaluates it. It tries to convert it into a number. In the next line,
f=str2func(fct)
you assume fct is a string.
To fix the problems, tell input to just return the user's input unchanged as a string (see the docs):
fct=input('enter your function in standard form: ', 's');