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C++ allows the char, int, and double data types to have modifiers preceding them. A modifier is used to alter the meaning of the base type so that it more precisely fits the needs of various situations.

The data type modifiers are listed here:

• signed
• unsigned
• long
• short

The modifiers signed, unsigned, long, and short can be applied to integer base types. In addition, signed and unsigned can be applied to char, and long can be applied to double.

The modifiers signed and unsigned can also be used as prefix to long or short modifiers. For example, unsigned long int.

C++ allows a shorthand notation for declaring unsigned, short, or long integers. You can simply use the word unsigned, short, or long, without the int. The int is implied. For example, the following two statements both declare unsigned integer variables.

unsigned x;
unsigned int y;

To understand the difference between the way that signed and unsigned integer modifiers are interpreted by C++, you should run the following short program:

#include <iostream>
using namespace std;
 
/* This program shows the difference between
 * signed and unsigned integers.
*/
int main() {
   short int i;           // a signed short integer
   short unsigned int j;  // an unsigned short integer

   j = 50000;

   i = j;
   cout << i << " " << j;

   return 0;
}

When this program is run, following is the output:

-15536 50000

The above result is because the bit pattern that represents 50,000 as a short unsigned integer is interpreted as -15,536 by a short.

Type Qualifiers in C++

The type qualifiers provide additional information about the variables they precede.

Qualifier	Meaning
const	Objects of type const cannot be changed by your program during execution
volatile	The modifier volatile tells the compiler that a variable's value may be changed in ways not explicitly specified by the program.
restrict	A pointer qualified by restrict is initially the only means by which the object it points to can be accessed. Only C99 adds a new type qualifier called restrict.