What does the unsigned keyword do here?

Question

I wrote some C++ code to show ASCII characters on a console which I found in a book i was reading. The code looked like this:

#include <iostream>

using namespace std;

int main()  
{  
    for (unsigned char i = 32; i<128; i++)  
       cout << i;  
    int response;  
    cin >> response;  
    return 0;  
}

When I take away the unsigned keyword and use signed instead, the results become infinite and the PC beeps until I shut off the executable file. But when I use an int i variable instead I don't need to unsign the variable. Why is that?

Answer 1

unsigned simply means that the number won't become negative. Yeah, number, because a char really is just an 8-bit integer.

So when unsigned, every bit is used in the non-negative range, which will go from 0 to 255. When you leave out and use a signed (default) char, the range will go from -128 to 127, thus it will always be less than 128 and go into an infinite loop.

The beep you hear is due to the char of value 7 being "printed".

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An int, on the other hand, even when signed goes all the way from -2.147... billions to +2.147 billions, so it will iterate normally until reaching 128 and stopping.