How do I modify my code to get rid of this error: "Index exceeds the number of array elements. Index must not exceed 1. Error in AEM614HW2Q2 (line 35) "

This is my error.

Index exceeds the number of array elements (1).

Error in HW2P2 (line 35)

C(j,n) = 2*b/(pi*c(j)) * sin(n*theta(j)) + n * sin(n*theta(j))/sin(theta(j));

clc; clear all; close all
N=500;
V_inf = 50;
i = 1;
lambda = .5; %linspace(0,1,N)
S = 39.2699;
AR = 10.1859;
alpha = 8; % Angle of Attack in degrees
b = 20;
alpha_0 = 0; % Zero lift angle of attack is 0 due to airfoil being symmetric
cr = (2*b)/(AR*(lambda+1));
ct = cr*lambda;
for theta = linspace(.001,pi-.001,20);
    y = (b/2)*cos(theta);
    if theta <= pi/2
        c = (2/b)*cr*(1-lambda)*y+cr;
    else
        c = -(2/b)*cr*(1-lambda)*abs(y)+cr;
    end
    alpha   = alpha   * pi/180;
    alpha_0 = alpha_0 * pi/180;
    if length(alpha) == 1
        alpha   = alpha * ones(N,1);
    end
    if length(alpha_0) == 1
        alpha_0 = alpha_0 * ones(N,1);
    end
    if length(c) == 1
        c       = c * ones(N,1);
    end
    C = zeros(N,N);
    B = zeros(N,1);
    for j = 1:N
        for n = 1:N
               C(j,n) = 2*b/(pi*c(j)) * sin(n*theta(j)) + n * sin(n*theta(j))/sin(theta(j));
        end
            B(j,1) = alpha(j,1) - alpha_0(j,1);
    end
    A = C\B;
    Gamma   = zeros(N,1);
    alpha_i = zeros(N,1);
    for j = 1:N
        for n = 1:N
            Gamma(j,1)   = Gamma(j,1) + 2*b*V_inf * A(n) * sin(n*theta(j));
            alpha_i(j,1) = alpha_i(j,1) +       n * A(n) * sin(n*theta(j))/sin(theta(j));
        end
    end
end
        A1(i) =A(1);
        Cl(i) = AR*pi*A1;
            

Answer 1

[David Hill]

C(j,n) = 2*b/(pi*c(j)) * sin(n*theta) + n * sin(n*theta)/sin(theta);%get rid of theta(j) theta is scalar, cannot index >1 into it

Answer 2

[Walter Roberson]

for theta = linspace(.001,pi-.001,20);

theta is a scalar

        for n = 1:N
               C(j,n) = 2*b/(pi*c(j)) * sin(n*theta(j)) + n * sin(n*theta(j))/sin(theta(j));
        end

but there theta has to be a vector of length N