%calculates the molecular weight of an molecule with C,N,H,O as elements
V = input('enter your molecule -it can only have C,N,H,0')
n = length(V);
k=1;
mol = 0;
disp('num will be the various numbers in the formula for the molecule')
while(k <= n)
    %look for the location of the next letter
    % the chars in between we convert into a number
    j = 1;
    while ( ((k+j)<= n)& isletter(V(k+j))==0)
        j=j+1;
    end;
    if (j == 1)
        num = 1;
    else
        num = str2num(V(k+1:k+j-1))
    end; %if
    if(V(k) == 'C') %determine weight of an element
        wt = 12;
    elseif (V(k) == 'N')
        wt = 14;
        elseif (V(k) == 'O')
        wt = 16;
        elseif (V(k) == 'H')
        wt = 1;
    end;
        
    mol=mol + num*wt;%add weight to running sum of weights
    k = k+j;
end;
 mol