Error using ==> sprintf Function is not defined for 'sym' inputs. How to solve this problem?

I found the below program abt Bisection Method to Find roots of a Equation in net.....

format long     %setting the number of digits to be displayed during the calculation
clc             %clears the screen
syms x;        %declaring x which wil be used as the independent parameter at the time to entry of function by the user

func = input('Please enter a expression for f(x):');       % prompting user to enter the function which will be stored in variable func
xl = input('Please enter the stating point of the interval :');       %prompting user to enter the starting point of the interval ,this will be stored in variable xl
xu = input('Please enter the end point of the interval :');             %prompting user to enter the end point of the interval ,this will be stored in variable xu
decimalplaces=input ('Please enter the number of decimal places :');    %prompting user to enter the tolerance level to the number of digits  ,this will be stored in variable decimaldigits
if(decimalplaces<0)                                 %checks for the wrong input of the user
    nullkey=input('Invalid Input!\nPress any key to continue');     %Error Message
    return          %program terminates
end

function_value_at_xl=subs(func,x,xl)            %stores function value at xl
function_value_at_xu=subs(func,x,xu)            %stores function value at xu
check_limits=function_value_at_xl*function_value_at_xu;     %product of function value at xl and xu
sprintf('f(%f)*f(%f) = %f',xl,xu,check_limits)      %displays the product
if(check_limits>0)              %checks if the root lies in the specified interval
    sprintf('Root does not lie in the given interval\nThe program will now terminate')      %error message
    nullkey=input('Press any key to continue');     %error message
    return      %program terminates
end
disp('So the root lies in the given interval')  %displays confirmation message

i=0;        %counts the number of iterations
while(1)    %infinite loop to do the required iterations
    disp('-------------------------------------------------------------------------------------------------')
    disp('Iteration =') %displays iteration number
    disp(i)             %displays iteration number
    sprintf('\nThe Interval is [%f,%f]',xl,xu)  %displays interval
    xr=(xl+xu)/2        %finds midpoint
    termination_check=abs(xl-xr);   %calculates the variable to be used for termination condition 
    sprintf('Termination Condition:\n|xl-xr| = |%f - %f| = %f ',xl,xr,termination_check)   %displays the termination condition
    if (termination_check<.5*10^-decimalplaces)  %if required accuracy is achieved loop beaks
        sprintf('---------------------------------------------------------------------------------------------\n---------------------------------------------------------------------------------------------\nAccuracy upto %f decimal places achived \n The Root of the given problem is = %f',decimalplaces,xr) %displays the root
        break
     end

      function_value_at_xr=subs(func,x,xr)    %stores function value at xr
      function_value_at_xl=subs(func,x,xl)    %stores function value at xl
      check=function_value_at_xr*function_value_at_xl;    %variable to check in which sub-interval the root lies
      sprintf('function value at xr * function value at xl=%f',check) %displays the value
      if(check<0)     %determines if the root is in lower sub interval
          disp('Therefore root lies in lower sub-interval')
          xu=xr   %then upper limit of next inteval is the mid-point  of the preceding interval
      end
      if (check>0)      %determines if the root is in upper sub interval
          disp('Therefore root lies in upper sub interval')
          xl=xr       %then lower limit of next inteval is the mid-point  of the preceding interval
      end

      i=i+1;  %increments the number of iterations

      disp('So we will do further iterations')
  end
  k=-5:1:5;       %x-axis variable to plot graph  from -5 to 5 
  y=subs(func,x,k);   %y-axis variable to plot graph  found out by substituting k in the given function
  plot(k,y)   %plotting function

but i can't able to run it. when going to sprint function it displays the below fig on command window:

Please enter a expression for f(x):x^2-x-1
Please enter the stating point of the interval :1
Please enter the end point of the interval :2
Please enter the number of decimal places :2

function_value_at_xl =

-1

function_value_at_xu =

1

Error using sprintf
Function is not defined for 'sym' inputs.

Error in BisectionMethod_1 (line 17)
sprintf('f(%f)*f(%f) = %f',xl,xu,check_limits)      %displays the product

What can i do regarding this problem? Any help or comments would be of great help! Thank you.