Unsigned int overflow in decrementing loops

A case study of interger overflow's impact on iterators. when an unsigned integer is used in decrementing "for" loops. The loop unexpectedly iterates indefinitely if the loop had to terminate when the value becomes lesser than 0.

for(unsigned int i = length; i >= 0; --i)
{
    //...
}

Since an unsigned integer is used, decrementing the variable to lesser than 0 will roll the value back to the

MAXIMUM_VALUE

that can be stored in the variable (depending on its size, usually 4 bytes - on 32 or 64 bit Windows), which is always >=0.

One possible solution is to terminate the loop when the value becomes greater than the initial assigned value or equal to the

MAXIMUM_VALUE

.

for(unsigned int i = length; i <= length; --i)
{
    //...
}

for(unsigned int i = length; i != MAXIMUM_VALUE; --i)
{
    //...
}

Another solution would be to reserve 0 for the terminating condition. Note that the length should not be equal to

MAXIMUM_VALUE

. Thus, a variable can be used to iterate a maximum count of

MAXIMUM_VALUE

.

for(unsigned int i = length + 1; i > 0; --i)
{
    //Use i-1 ...
}

But, why use unsigned int at all? a signed integer does not have this problem. Because, unsigned integer have wider positive values range than the signed integer.

positive value range for signed integer: 0 to std::numeric_limits<signed  int >::max()
positive value range for unsigned integer: 0 to std::numeric_limits<unsigned  int >::max()

where, std::numeric_limits<signed  int >::max() <  std::numeric_limits<unsigned  int >::max()