Question

What is the difference between sizeof(3.0) and sizeof(3.0f)

I was expecting both of them to give the same result (sizeof float)..but its different.

In 32 bit machine,gcc compiler,
sizeof(3.0f) =>4
sizeof(3.0) => 8

Why so?

Answer 1

Because 3.0 is a double. See C syntax Floating point types.

Floating-point constants may be
written in decimal notation, e.g.
1.23. Scientific notation may be used by adding e or E followed by a decimal
exponent, e.g. 1.23e2 (which has the
value 123). Either a decimal point or
an exponent is required (otherwise,
the number is an integer constant).
C99 introduced hexadecimal
floating-point constants, which follow
similar rules except that they must be
prefixed by 0x and use p to specify a
hexadecimal exponent. Both decimal and
hexadecimal floating-point constants
may be suffixed by f or F to indicate
a constant of type float, by l or L to
indicate type long double, or left
unsuffixed for a double constant.