Signed and Unsigned Types

Except for bool and the extended character types, the integral typesmay be signed or unsigned. A signed type represents negative or positive numbers (including zero); an unsigned type represents only values greater than or equal to zero.

The types int, short, long, and long long are all signed. We obtain the corresponding unsigned type by adding unsigned to the type, such as unsigned long. The type unsigned int may be abbreviated as unsigned.

Unlike the other integer types, there are three distinct basic character types: char, signed char, and unsigned char. In particular, char is not the same type as signed char. Although there are three character types, there are only two representations: signed and unsigned. The (plain) char type uses one of these representations. Which of the other two character representations is equivalent to char depends on the compiler.

In an unsigned type, all the bits represent the value. For example, an 8-bit unsigned char can hold the values from 0 through 255 inclusive.

The standard does not define how signed types are represented, but does specify that the range should be evenly divided between positive and negative values. Hence, an 8-bit signed char is guaranteed to be able to hold values from –127 through 127; most modern machines use representations that allow values from –128 through 127.

ADVICE: DECIDING WHICH TYPE TO USE

C++(www.cppentry.com), like C, is designed to let programs get close to the hardware when necessary. The arithmetic types are defined to cater to the peculiarities of various kinds of hardware. Accordingly, the number of arithmetic types in C++(www.cppentry.com) can be bewildering. Most programmers can (and should) ignore these complexities by restricting the types they use. A few rules of thumb can be useful in deciding which type to use:

.. Use an unsigned type when you know that the values cannot be negative.

.. Use int for integer arithmetic. short is usually too small and, in practice, long often has the same size as int. If your data values are larger than the minimum guaranteed size of an int, then use long long.

.. Do not use plain char or bool in arithmetic expressions. Use them only to hold characters or truth values. Computations using char are especially problematic because char is signed on some machines and unsigned on others. If you need a tiny integer, explicitly specify either signed char or unsigned char.

.. Use double for floating-point computations; float usually does not have enough precision, and the cost of double-precision calculations versus singleprecision is negligible. In fact, on some machines, double-precision operations are faster than single. The precision offered by long double usually is unnecessary and often entails considerable run-time cost.
EXERCISES SECTION 2.1.1

Exercise 2.1: What are the differences between int, long, long long, and short Between an unsigned and a signed type Between a float and a double

Exercise 2.2: To calculate amortgage payment, what typeswould you use for the rate, principal, and payment Explain why you selected each type.