why I get error using stem?

geometry geometry

2018 3 19

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I tried this code to stem the convolution of two discrete time signals x and h without using conv function.

but I get error entering x and h which are commented in the code. how can I fix it?

syms x h myconv n
myconv=0;
% x(n)=(n==0|n==4)-2*heaviside(n+3)+2*heaviside(n-3);
% y(n) = (n==0|n==4)-2*heaviside(n+3)+2*heaviside(n-3)-(-2*heaviside(2*n+5)+2*heaviside(2*n-1));
H(n)=heaviside(n)+(1/2)*piecewise(n==0,1,0);
x=input('Enter x: '); 
h=input('Enter h: ') ;
h = symfun(eval(h), n);
x = symfun(eval(x), n);
h = matlabFunction(h);
x = matlabFunction(x);
for i=-1000:1:1000
    myconv=x(i)*h(n-i)+myconv;
end
stem(N, subs(myconv,n,N), 'ko');