Objective-C Constants

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called pterals.

Constants can be of any of the basic data types pke an integer constant, a floating constant, a character constant, or a string pteral. There are also enumeration constants as well.

The constants are treated just pke regular variables except that their values cannot be modified after their definition.

Integer Literals

An integer pteral can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

An integer pteral can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer pterals −

212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */
078         /* Illegal: 8 is not an octal digit */
032UU       /* Illegal: cannot repeat a suffix */

Following are other examples of various types of Integer pterals −

85         /* decimal */
0213       /* octal */
0x4b       /* hexadecimal */
30         /* int */
30u        /* unsigned int */
30l        /* long */
30ul       /* unsigned long */

Floating-point Literals

A floating-point pteral has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point pterals either in decimal form or exponential form.

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Here are some examples of floating-point pterals −

3.14159       /* Legal */
314159E-5L    /* Legal */
510E          /* Illegal: incomplete exponent */
210f          /* Illegal: no decimal or exponent */
.e55          /* Illegal: missing integer or fraction */

Character Constants

Character pterals are enclosed in single quotes e.g., x and can be stored in a simple variable of char type.

A character pteral can be a plain character (e.g., x ), an escape sequence (e.g., ), or a universal character (e.g., u02C0 ).

There are certain characters in C when they are proceeded by a backslash they will have special meaning and they are used to represent pke newpne ( ) or tab ( ). Here, you have a pst of some of such escape sequence codes −

Following is the example to show few escape sequence characters −

#import <Foundation/Foundation.h>

int main() {
   NSLog(@"Hello	World

");
   return 0;
}

2013-09-07 22:17:17.923 demo[17871] Hello	World

"hello, dear"

"hello, 

dear"

"hello, " "d" "ear"

#define identifier value

#import <Foundation/Foundation.h>

#define LENGTH 10   
#define WIDTH  5
#define NEWLINE  
 

int main() {
   int area;
   area = LENGTH * WIDTH;
   NSLog(@"value of area : %d", area);
   NSLog(@"%c", NEWLINE);

   return 0;
}

2013-09-07 22:18:16.637 demo[21460] value of area : 50
2013-09-07 22:18:16.638 demo[21460] 

const type variable = value;

#import <Foundation/Foundation.h>

int main() {
   const int  LENGTH = 10;
   const int  WIDTH  = 5;
   const char NEWLINE =  
 ;
   int area;  
   
   area = LENGTH * WIDTH;
   NSLog(@"value of area : %d", area);
   NSLog(@"%c", NEWLINE);

   return 0;
}

2013-09-07 22:19:24.780 demo[25621] value of area : 50
2013-09-07 22:19:24.781 demo[25621]