why can't you assign a number with a decimal point to decimal type directly without using type suffix?

Question

Why can\'t you assign a number with a decimal point to the decimal type directly without using type suffix? isn\'t this kind of number considered a number of type decimal?

Answer 1

Actually, hidden spec feature: you can ;-p

decimal bankBalance = (decimal)3433.20;

This is genuinely parsed by the compiler as a decimal (not a float and a cast). See the IL to prove it. Note that the precision gets truncated, though (this has 1 decimal digit, not the 2 you get from the M version).

IL generated:

L_0001: ldc.i4 0x861c
L_0006: ldc.i4.0 
L_0007: ldc.i4.0 
L_0008: ldc.i4.0 
L_0009: ldc.i4.1 
L_000a: newobj instance void [mscorlib]System.Decimal::.ctor(int32, int32, int32, bool, uint8)
L_000f: stloc.0 

Compared to:

decimal bankBalance = 3433.20M;

Which generates:

L_0001: ldc.i4 0x53d18
L_0006: ldc.i4.0 
L_0007: ldc.i4.0 
L_0008: ldc.i4.0 
L_0009: ldc.i4.2 
L_000a: newobj instance void [mscorlib]System.Decimal::.ctor(int32, int32, int32, bool, uint8)
L_000f: stloc.0 

The only difference is the decimal digits (1 vs 2, and a factor of 10, accordingly)