C++ for Scientists - Technische Universität Dresden

22 CHAPTER 2. C++ BASICS
In the first case, we have an int literal that is converted into float and in the second case, the
literal is float from the beginning. For the sake of clarity, the float literal is preferable.
Later in this book we will introduce function overloading, that is a function with different
implementations for different argument types (or argument tuples). The compiler selects the
function overload that fits best. Sometimes the best fit is not clear, for instance if function f
accepts an unsigned or a pointer and we call:
f(0);
“0” is considered as int and can be implicitly converted into unsigned or any pointer type. None
of the conversions is prioritized. As before we can address the issue by explicit conversion and
by a literal of the desired type:
f(unsigned(0));
f(0u);
Again, we prefer the second version because it is more direct (and shorter).
The accuracy issue comes up when work with long double. On the author’s computer, the format
can handle at least 19 digits. Let us define one third with 20 digits and print out 19 of it:
long double third= 0.3333333333333333333;
cout.precision(19);
cout ≪ ”One third is ” ≪ third ≪ ”.\n”;
The result is:
One third is 0.3333333333333333148.
The program behavior is more satisfying if we append an “l” to the number:
long double third= 0.3333333333333333333l;
yielding the print-out that we hoped for:
One third is 0.3333333333333333333.
The following table gives examples of literals and their type:
Literal Type
2 int
2u unsigned
2l long
2ul unsigned long
2.0 double
2.0f float
2.0l long double
For more details, see for instance [Str97, § 4.4f,§ C.4]. There you also find a description how to
define literals on an octal or hexadecimal basis.