how to prevent overwriting in matrix while creating in for loop?

T(1,1) = (a-b-c);
T(1,2)=b;
T(2,1) = c;
C(1) = a*To;
for j= 2:1:nx-1
    i=1;
%middle nodes

T(i,j-1) = b/2;
T(i,j) = 2*a-b-2*c;
T(i,j+1) = b/2;
T (i+1,j+1) = 2*c;
C(j) = 2*a*To;
   T(i,j)=0;
end
%end node
T(1,nx-1) = b;
T(1,nx) = b + c + a;
T(2,nx) = c;
C(nx) = a*To;

%sliding
for i = 2:1:nysl

for j= 2:1:nx
 if(i<=nysl-1 && j==1);
    T(i-1,j)=1;
    T(i,j)= -4;
    T(i+1,j)=1;
    T(i,j+1)=2;

elseif (i<=nysl-1 && j<=nx-1);
    T(i-1,j) =1;
T (i,j-1) =1;
T(i,j) =-4;
T(i,j+1)= 1;
T(i+2,j)=1;
elseif (i<=nysl-1 && j==nx);
T(i-1,j) =1;
T (i,j-1) =2;
T(i,j) =-4;
T(i+1,j)= 1;
   else
   T(i,j)=0;
 end
end
end

while creating the matrix the successive operation overwrites the values allocated previously.Is there anyway to void the overwriting?

[Stephen23]

"Is there anyway to avoid the overwriting?"

Yes. Simply preallocate an output array of the correct size, and use indexing to assign the new values within the loop. You will find lots of examples online.