to build a histogram

Hi everybody. I need a help. I'm trying to make a histogram which the average value must be zero. So, I'm not getting a histogram which has in axis-x both values positives and negatives.

This is the function which I'm using:

function freqDT = htgDT(da,det)

      % Chamamos a função dife para realizar a diferença de tempo. Ela retorna uma matriz com as diferenaças    
      DF=dife(da,det);
      b=size(DF);
      MDT=zeros(2001,b(1,2)); %A quantidade de diferenças corresponderá a quantidade de colunas de DF

      for y =1:b(1,2) %y varia conforme a quantidade de diferenças
          for x = 1:b(1,1)
              c = DF(x,y); 
              if c == 0
                  MDT(1,y)=MDT(1,y) + 1;
              end
              if c>0 && c<1000
                  MDT(c+1,y)=MDT(c+1,y) + 1;
              end
         %%%%%%%%%%%%%%the probleme is here%%%%%%%%%%%%
              if c<0 && abs(c)<1000
                  %x
                  %M=abs(c)+1000

                  MDT(abs(c)+1000,y)= MDT(abs(c)+1000,y) + 1;
              end
          %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
           end
      end
    freqDT = MDT;
  end