Should unsigned ints be used if not necessary?

Question

Should one ever declare a variable as an unsigned int if they don\'t require the extra range of values? For example, when declaring the variable in a for loop, if you know i

Answer 1

Even if you have variables that should only take non negative values unsigned can be a problem. Here is an example. Suppose a programmer is asked to write a code to print all pairs of integer numbers (a,b) with 0 <= a < b <= n where n is a given input. An incorrect code is

for (unsigned b = 0; b <= n; b++)
   for (unsigned a=0; a <=b-1; b++)
       cout << a << ',' << b << n ;

This is easy to correct, but thinking with unsigned is a bit less natural than thinking with int.