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Asked: 2026-06-01T19:49:43+00:00

This feels like a stupid question, but I can’t seem to see the answer.

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This feels like a stupid question, but I can’t seem to see the answer. I have an UInt64, which is supposed to have a max value of 

UInt64.MaxValue 18446744073709551615

However, when I try to assign a modest-sized number, I get this overflow error of “The operation overflows at compile time in checked mode”. If I wrap it in an “unchecked” block then it compiles, and runs as if this variable is zero:

UInt64 value1 = 1073741824 * 8; // Compile error CS0220
UInt64 value2 = 8589934592;     // Actual value - no error

Why is this happenning?

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1 Answer

  1. Editorial Team

    Because:

    UInt64 value1 = 1073741824 * 8;

    Is doing the arithmetic as a signed 32-bit integer, then converting it to an ulong. Try:

    UInt64 value1 = 1073741824UL * 8;

    The UL means that the literal is of an unsigned long. See section 2.4.4 of the C# Specification for more on literal suffixes:

    If the literal is suffixed by UL, Ul, uL, ul, LU, Lu, lU, or lu, it is of type ulong

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