Scanf function changes value of in-loop variable

[Capture_A_Lag]

Hi all!
I have this code:

------------------------------------------------------------------------------
ubyte N, M, K;
ubyte[][max][max] Matrix;
scanf("%d %d %d", &N, &M, &K);

ubyte tmp;

for(ubyte n = 1; n <= N; n++)
        for(ubyte m = 1; m <= M; m++)
        {
                scanf("%d", &tmp);
                // After this scanf n becomes 0 for no reason
                
                if(tmp) Matrix[m][tmp] ~= n;
        }

------------------------------------------------------------------------------

After scanf in loop variable n becomes 0. Is this a bug? Please 
help me!