• Only for quantities that are never negative (B-1)
  • (B-1) Such as populations and bean counts

To create unsigned versions of the basic integer types

• You just use the keyword unsigned to modify the declarations (A-1):

Example of (A-1)

unsigned short change;		// unsigned short type
unsigned int univac; 		// unsigned int type
unsigned eniac;			// also unsigned int
unsigned long edvac;		// unsigned long type

Note that unsigned by itself

• Is short for unsigned int

(A-2) illustrates the use of unsigned types

• It also shows you what happen if your program tries to go beyond the limits for integer types (B-2)
• (B-2) Finally, it gives you one last look at the preprocessor # define statement

Example of (A-2)

#include <iostream>
#define ZERO 0	// makes ZERO symbol for 0 value
#include <climits>	// defines INT_MAX as largest int value
 
int main()
{
	using namespace std;
	short johnPresperEckert = SHRT_MAX;			// initialize a variable to max value
	unsigned short johnWilliamMauchly = johnPresperEckert;	// okay if variable johnPresperEckert already defined
 
	cout << "Eckert has " << johnPresperEckert << " dollars and Mauchly has " << johnWilliamMauchly;
	cout << " dollars deposited." << endl
		 << " Add $1 to each account. "<< endl << "Now ";
	johnPresperEckert = johnPresperEckert + 1;
	johnWilliamMauchly = johnWilliamMauchly + 1;
	cout << "Eckert has " << johnPresperEckert << " dollars and Mauchly has " << johnWilliamMauchly;
	cout << " dollars deposited.\nPoor Eckert." << endl;
	johnPresperEckert = ZERO;
	johnWilliamMauchly = ZERO;
	cout << "Eckert has " << johnPresperEckert << " dollars and Mauchly has " << johnWilliamMauchly;
	cout << " dollars deposited." << endl
		 << " Take $1 from each account. "<< endl << "Now ";
	johnPresperEckert = johnPresperEckert - 1;
	johnWilliamMauchly = johnWilliamMauchly - 1;
	cout << "Eckert has " << johnPresperEckert << " dollars and Mauchly has " << johnWilliamMauchly;
	cout << " dollars deposited." << endl << "Lucky Mauchly" << endl;
	return 0;
}

Compatibility Note

• The example (A-2), uses the climits file; older compilers might need to use limits.h, and some very old compilers might not have either file available

Here’s the output from the program in (A-2):

The program

• Sets a short variable (johnPresperEckert) and an unsigned short variable (johnWilliamMauchly) to the largest short value, which is 32,767 on our system (B-3)
• (B-3) Then it adds 1 to each value (B-4)
• (B-4) This causes no problems for johnWilliamMauchly because the new value is still much less than the maximum value for an unsigned integer (B-5)
• (B-5) But johnPresperEckert goes from 32,767 to -32,768 (B-6)
• (B-6) Similarly, subtracting 1 from 1 from 0 creates no problems for johnPresperEckert, but it makes the unsigned variable johnWilliamMauchly go from 0 to 65,535 (B-7)
• (B-7) As you can see, these integers behave much like an odometers (B-8)
• (B-8) If you go past the limit, the values just start over at the other end of the range
  • (Image-1) C++ guarantees that unsigned types behave in this fashion
  • However, C++ doesn’t guarantee that signed integer types can exceed their limits (overflow and underflow) without complaint, but that is the most common behavior on current implementations

(Image-1) Typical overflow behavior for integers

Beyond long

• C99 has added a couple new types that most likely will be part of the next edition of the C++ Standard (B-9)
  • Indeed, many C++ compilers already support them
  • (B-9) The types are long long and unsigned long long. Both are guaranteed to be at least 64 bits and to be at least as wide as the long and unsigned long types

• Which is a group of 16 contiguous bits or 2 bytes, is used to represent a natural number
• As we have studied, the maximum numeric value that can fit in a word is 65535
• Since the Byte is used only to represent a character, whenever you plan to use a number in your program, the minimum representation you should/must use is a word

An algebraic natural number

• Is also called an integer

The smallest integer you can store in a word

• Is declared with the short keyword followed by a name

A short integer is signed by default

• It can store a value that ranges from –32768 to 32767
• Here is an example program that uses two short integers (A-1):

Example of (A-1)

#include <iostream>
 
using namespace std;
 
int main()
{
 
	short number1, number2;
 
 
	cout << "Enter a number between -32768 and 32767: ";
 
	cin >> number1;
 
	cout << "Enter another number: ";
 
	cin >> number2;
 
 
 
	cout << "\nThe numbers you entered were\n";
 
	cout << "\tNumber 1: " << number1 << "\n";
 
	cout << "\tNumber 2: " << number2 << "\n";
 
 
 
	return 0;
 
}

 
By default, a short integer

• Is signed
• You can also explicitly declare such a variable as a signed short
• Here is an example (A-2):

 
Example of (A-2)

signed short XCoord;

If the integer must be positive

• You should declared as an unsigned short

The unsigned short is used

• To identify a 16-bit positive integer whose value would range from 0 to 65535