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A floating-point constant must have either a decimal point, an exponent-of-ten, or both; they distinguish it from an integer constant.
To indicate an exponent, write ‘e’ or ‘E’. The exponent value follows. It is always written as a decimal number; it can optionally start with a sign. The exponent n means to multiply the constant’s value by ten to the nth power.
Thus, ‘1500.0’, ‘15e2’, ‘15e+2’, ‘15.0e2’, ‘1.5e+3’, ‘.15e4’, and ‘15000e-1’ are six ways of writing a floating-point number whose value is 1500. They are all equivalent in principle.
Here are more examples with decimal points:
1.0 1000. 3.14159 .05 .0005
For each of them, here are some equivalent constants written with exponents:
1e0, 1.0000e0 100e1, 100e+1, 100E+1, 1e3, 10000e-1 3.14159e0 5e-2, .0005e+2, 5E-2, .0005E2 .05e-2
A floating-point constant normally has type double
. You can
force it to type float
by adding ‘f’ or ‘F’
at the end. For example,
3.14159f 3.14159e0f 1000.f 100E1F .0005f .05e-2f
Likewise, ‘l’ or ‘L’ at the end forces the constant
to type long double
.
You can use exponents in hexadecimal floating constants, but since ‘e’ would be interpreted as a hexadecimal digit, the character ‘p’ or ‘P’ (for “power”) indicates an exponent.
The exponent in a hexadecimal floating constant is an optionally signed decimal integer that specifies a power of 2 (not 10 or 16) to multiply into the number.
Here are some examples:
0xAp2 // 40 in decimal 0xAp-1 // 5 in decimal 0x2.0Bp4 // 32.6875 decimal 0xE.2p3 // 113 decimal 0x123.ABCp0 // 291.6708984375 in decimal 0x123.ABCp4 // 4666.734375 in decimal 0x100p-8 // 1 0x10p-4 // 1 0x1p+4 // 16 0x1p+8 // 256
See Floating-Point Data Types.
Next: Imaginary Constants, Previous: Integer Const Type, Up: Constants [Contents][Index]