How to calculate qammod for discrete time using for-loop?

Hello,i want to use the function qammod to create a 4-QAM signal.

I want to create 4-QAM for the signal y[k] ,k=1,...N (N=100) . The code is for qammod is simple:

M = 4;

x = (0:M-1)';

y = qammod(x,M);

scatterplot(y)

I want to run this for the length of k , so i use for-loop (for i=1:length(k)) .But when i try to find:

y(i) = qammod(x,M);

i keep getting the message :In an assignment A(I) = B, the number of elements in B and I must be the same .

Can anyone help me with this for loop?

Thank you.