Unsigned integer in C ++
I am writing the following code:
#include <iostream>
using namespace std;
int main() {
unsigned int i=1;
i=i-3;
cout<<i;
return 0;
}
The output is the meaning of garbage, which is understandable.
Now I am writing the following code:
#include <iostream>
using namespace std;
int main() {
unsigned int i=1;
i=i-3;
i=i+5;
cout<<i;
return 0;
}
The result is now 3. What's going on here? How is the garbage cost added by 5 here?
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Think of the values unsigned int
drawn on the large edge of the counter with the largest possible value (UINT_MAX), near zero.
Subtracting 3 from 1 moves you 3 spaces back (which gives you UINT_MAX - 1), and adding 5 to that moves you 5 spaces forward.
The net effect is to add 2 to 1, but it's important to know that the intermediate value is perfectly defined by the C ++ standard. This is not garbage, but related to the value UINT_MAX
on your platform.
Note that the well-defined nature of this overflow is incorrect for types signed
. Type overflow behavior signed
is undefined in C ++.
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