How to cast or convert an unsigned int to int in C?

Question

My apologies if the question seems weird. I'm debugging my code and this seems to be the problem, but I'm not sure.

Thanks!

Answer 1

It depends on what you want the behaviour to be. An int cannot hold many of the values that an unsigned int can.

You can cast as usual:

int signedInt = (int) myUnsigned; 

but this will cause problems if the unsigned value is past the max int can hold. This means half of the possible unsigned values will result in erroneous behaviour unless you specifically watch out for it.

You should probably reexamine how you store values in the first place if you're having to convert for no good reason.

EDIT: As mentioned by ProdigySim in the comments, the maximum value is platform dependent. But you can access it with INT_MAX and UINT_MAX.

For the usual 4-byte types:

4 bytes = (4*8) bits = 32 bits 

If all 32 bits are used, as in unsigned, the maximum value will be 2^32 - 1, or 4,294,967,295.

A signed int effectively sacrifices one bit for the sign, so the maximum value will be 2^31 - 1, or 2,147,483,647. Note that this is half of the other value.

Answer 2

Unsigned int can be converted to signed (or vice-versa) by simple expression as shown below :

unsigned int z; int y=5; z= (unsigned int)y;    

Though not targeted to the question, you would like to read following links :

• signed to unsigned conversion in C - is it always safe?
• performance of unsigned vs signed integers
• Unsigned and signed values in C
• What type-conversions are happening?