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Compare and Logical operators - boolean data type

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• The Boolean data type in C (or the lack there of)
  • Before 1999, the C programming language does not have any boolean (logic) data type

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  • C99 (see Wikipedia page: click here) introduced the

    _Bool

    data type that is not available in other C derivates (like C++)

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  • This data type is nothing more than an ordinary int with some macro definition support for boolean values (like true and false

    Take a look at /usr/include/stdbool.h:

    #define bool _Bool #define true 1 #define false 0

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  • Bottom line:

    You may well say that: C does not provide a (genuine) boolean data type Traditionally, the C programming language uses integer types to represent boolean data types

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• Boolean values (constants)
  • Boolean values (in general)

    Unlike Java, the C programming language does not define Boolean values BTW, the Boolean values in Java are defined using the keywords: true false Example: Java: boolean a; a = true;

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  • Boolean values in C:

    0 = false Any other value = true

    Example: the following if-statement will print "value is true"

    if ( 1 ) printf("value is true\n"); /* Because 1 is not ZERO, so "true" */ else printf("value is false\n");

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   gcc logic1.c To run:          ./a.out

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• How to use boolean data type in C
  • Important to remember in C:

    C does not have an genuine boolean data type The _Bool data type is a half hearted implemention of the boolean data type Does not come close to a real data type. How to use boolean type in C: If you need a boolean variable, define an integer type (char, short, int..) variable instead Use any numerical (integer) value that is not equal to ZERO (0) to represent true (usually, people will use 1) Use only the numerical value 0 to represent false

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• Compare operators in C
  • Fact:

    Compare operators in C behave the same way as those in Java.... if you interpret the result of the compare operators as follows: 1 to represent true 0 to represent false

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  • Summary of the compare operators in C

    Compare operations | Meaning ---------------------+----------------------------------------------------- x == y | returns 1 if x is equals to y, returns 0 otherwise x != y | Not equal x < y | Less than x <= y | Less than or equal x > y | Greater than x >= y | Greater than or equal

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• Logical operators in C
  • Fact:

    Logical operators in C behave the same way as those in Java.... if you interpret the result of the compare operators as follows: 1 to represent true 0 to represent false

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  • Summary of the logical operators in C

    Compare operations | Meaning ---------------------+----------------------------------------------------- x && y | returns 1 if "x and y" is true, returns 0 otherwise x || y | logical or !x | logical not

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

    How to run the program:

    Right click on link and save in a scratch directory To compile:   gcc logic2.c To run:          ./a.out