How to assemble Kglobal in a for loop?

Trying to solve a FEM problem using given data and a for loop to run for each node's stiffness matrix. I think I need to index each K matrix as the loop runs, but currently, I can only get the last variable of K, and it is not indexing into the Kglobal matrix. Any help would be appreciated.

    % clc 
%%Input Text Files
connectivity_data = dlmread('connectivity.txt');
forces_data = dlmread('forces.txt')';
boundaryconditions_data = dlmread('boundaryconditions.txt');
%%Enter in functions to extract needed rows and columns from .txt files
irow = connectivity_data(:,2);
jcolumn = connectivity_data(:,3);
L = transpose(connectivity_data(:,5));
theta = connectivity_data(:,4);
index = 2*((numel(connectivity_data(:,1)))-1);
nelement = length(connectivity_data(:,4));
%%Enter in degrees of freedom and # of nodes
ndof = 2;
nnodes = (nelement-1);
%%Input Constants needed to solve for connectivity_data matrix
E = 3e7;
A = 4;
EA = E*A;
%%Input Forces 
%%Assign a K for each element using formula K=(E*A)/L
% E*A will remain constant, while L will change at each node
% K = (EA)./(in);
%%Establish for loop to calculate Stiffness Matrix for each element
K = zeros(ndof*nnodes)
for (i = 1:nelement)
    theta = connectivity_data(i,4);
    C = cosd(theta);
    S = sind(theta);
    U = [C.^2 C.*S -C.^2 -C.*S;
        C.*S S.^2 -C.*S -S.^2;
        -C.^2 -C.*S C.^2 C.*S;
        -C.*S -S.^2 C.*S S.^2 ];
    L = connectivity_data(i,5);
    K = ((EA)/L)*U;
    KG(index,1) = K(1,1);
end

Answer 1

[Steven Lord]

for (i = 1:nelement)

Remove the parentheses.

      theta = connectivity_data(i,4);
      C = cosd(theta);
      S = sind(theta);
      U = [C.^2 C.*S -C.^2 -C.*S;
          C.*S S.^2 -C.*S -S.^2;
          -C.^2 -C.*S C.^2 C.*S;
          -C.*S -S.^2 C.*S S.^2 ];
      L = connectivity_data(i,5);
      K = ((EA)/L)*U;
      KG(index,1) = K(1,1);

Where in this loop does the variable index change its value? Did you mean to use i instead of index in determining the element in KG into which to write K(1, 1)?

end

[Edmund Valdez]

Fixing the index/i mixup is now giving me values in my KG matrix. I still am not seeing the correct KG values, although the values I calculated K for each individual stiffness matrix are correct and match previous data.

    % for i = 1:nelement
    theta = connectivity_data(i,4);
    C = cosd(theta);
    S = sind(theta);
    U = [C.^2 C.*S -C.^2 -C.*S;
        C.*S S.^2 -C.*S -S.^2;
        -C.^2 -C.*S C.^2 C.*S;
        -C.*S -S.^2 C.*S S.^2 ];
    L = connectivity_data(i,5);
    K = ((EA)/L)*U
    KG(i,1) = K(1,1);
end