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cprintfmultiplication16-bit

Weird Output for Printf Unsigned Long

This one is simple.

printf("%lu\n", (unsigned long)(320 * 200));

That line of code prints out "4294965760". That is definitely NOT equal to 360 * 200. What's wrong with it?

I am using Digital Mars C compiler in 16 bit medium memory model.

Solution

  • On a 16-bit system, if sizeof(int) == 2, then 320 * 200, which is equal to 64000, is too big for a signed int (range ±32,767 — and usually -32,768 too, but in theory it varies by platform). So, you have arithmetic overflow. The cast doesn't affect the multiplication; it only affects what happens to the result of the multiplication.

    You'd do better with:

    printf("%lu\n", 320UL * 200UL);

    That forces the constants to unsigned long.