how i create a free dimension variable like array or cell variable?

i want initialized a matrix or cell with a series of repeatedly inputs that number of every input is random, when i do not create a assumption matrix like a=zeros(m,n) and then initialized whit inputs i receive this error: Index exceeds matrix dimensions. (because has been created a matrix with dimension size of last input and often number of inputs every time change.) and but because i do not know number of all inputs i can not create a fix dimension matrix like a=zeros(m,n) now i want have a matrix whit free dimension?