Boolean in C
Since the computers operate on 0’s(False) and 1’s(True) computer logic is also expressed in boolean terms and all the complex logic of computers and digital systems is evaluated by using boolean algebra to take the particular decisions. So through this article, we will discuss the significance of Boolean in context with one of the most popular computer languages C.
Why do We Need Boolean Values?
Computers and other Digital Systems only think in terms of ON(True) or OFF(False) , whereas we humans use a very diverse set of symbols in our daily life apart from these two terms. But when there comes a situation to make a decision, we only think in terms of Yes(True) or No(False) statements, which is nothing but a Boolean. Yes, you heard right, it’s Boolean. Boolean or boolean logic is a subset of algebra used for creating True or False statements. The term Boolean Algebra is named after the great mathematician George Boole. Hence, any kind of logic, expressions, or work theories by George Boole is considered Boolean .
Boolean Data Type in C
In C the terminology of boolean is associated with data type and Boolean is termed as one of the data types in the C Standard Library. This data type stores one of the two possible values denoted by true or false, which represents two truth values of logic and Boolean Algebra. All non-zero values are treated as true, while 0 is treated as false .
Though the boolean only stores true or false values, they are really very important in programming because they allow us to control the flow of code in different situations. In C, the Boolean data type can be invoked after including the "stdbool.h" header file. It means the C program will give a compilation error if we directly try to use boolean data type without including the stdbool.h header, whereas in C++, we do not have to include any extra headers .
Syntax to Declare Boolean Data Types in C:
To declare a boolean data type in C, we have to use a keyword named bool followed by a variable name.
Here, bool is the keyword denoting the data type and var_name is the variable name.
A bool takes in real 1 bit, as we need only 2 different values(0 or 1). So the sizeof (var_name) will give the result as 1 i.e. 1byte is required to store a boolean value and other 7 bits will be stuffed with 0 values.
Now let’s see a small example to understand the application of boolean data type in C.
Example of Boolean in C ( using stdbool.h header ):
In the above example, we have included the stdbool.h header file as we are using the bool type variable in our program, then we have declared a variable x of type boolean using bool and initialized it with value false. After that, we applied the condition checks using the if-else block to determine if the value of variable x is true or false.
What if we forgot the name of the header file to include for using boolean data type or what if we don’t want to include any extra header in our program but want to use boolean data type?
Well, we know that C doesn’t provide us with a boolean as a predefined data type. In such a scenario, we will have to create our custom data type, which will behave the same as shown in the previous example. To do this we can leverage the power of keyword typedef and enumeration ( enum ) in C.
Let’s understand this with an example.
Example of Boolean in C ( using typedef ):
Isn’t it simple? Let’s try to understand what we have implemented in the above example.
enum (enumeration) is a user-defined data type in C used to assign names to integer constants. In our case, we have assigned false to constant 0 state and true to constant 1 state using enum .
The typedef keyword is used to give a symbolic name to the type and is automatically interpreted by the compiler. In our case, we have assigned it as a bool_enum.
Hence, now we can use this custom type bool_enum which will behave the same as that of the boolean data type from the stdbool.h header file.
Boolean Arrays in C:
Like normal arrays, we can also create the boolean arrays using the data type bool from stdbool.h header file in C. The boolean array can store multiple true or false values for each element and all elements and can be accessed by using indexes.
Let’s see a small example to declare, initialize and print all elements from a boolean array. Through this example, we will try to initialize true value to all even indexed elements and false to all odd indexed elements.
In the above example, we have declared the boolean array and initialized all even index elements with true values and odd index elements with false values. Then we tried accessing those values based on indexes and tried printing them to the console.
Boolean and Logical Operators:
The Boolean data type when used with conditional statements like if..else ladders or simple if..else gives us the opportunity to choose specific actions by changing the control flow depending on the specified Boolean conditions (true or false) . At a time of evaluating conditions using if statements, it is often helpful to be able to do multiple comparisons at one time to limit the number of if statements used in our code, which allows us to write cleaner, concise, and more readable code .
Hence, if we want to perform multiple comparisons at one time, we need to understand how our computer interprets true and false values. When our computer encounters true or false, it assigns them numeric values of 1 or 0 respectively. Then the computer applies a set of logic based on Boolean Algebra. Boolean Algebra sets out the rules of what results to expect when combining multiple boolean logics with operators.
While performing Boolean logic, the expression on the left is evaluated, followed by the expression on the right. The two expressions are finally evaluated in the context of the logical operator between them. The return value is of Boolean type and is based on the operator type used.
There are Three Types of Logical Operators in the C Language:
We have already seen that Operators need some boolean conditions or boolean results to act upon. So for more clarity, we will assume set A and set B represent two independent boolean conditions or boolean results, and we will use them to understand the behavior of the boolean operators.
1. && (AND) Operator in C: The && (AND) operator is C also known as logical conjunction and requires both left-side expression and right-side expression to be true for the result to be true. All other cases results are false. This is logically the same as the intersection of two sets.
The truth table for the && (AND) Operator is given below,
Where A denotes the expression on the left side of the operator and B denotes the expression on the right side of the operator.
2. || (OR) Operator in C: The || (OR) operator in C requires only one of the boolean logic to be true for the result to be true. This is equivalent to the union of two sets.
The truth table for the || (AND) Operator is given below,
Where A denotes the expression on the left side of the operator and B denotes the expression on the right side of the operator.
Short-Circuiting:
There is a concept that is closely associated with the && (AND) and || (OR) operators named Short-Circuiting. It is a compiler optimization technique to avoid evaluating an unnecessary expression. As expressions are evaluated from left to right, there are some expressions that are calculated certainly by only evaluating parts of the expression. This technique detects such expressions and helps the compiler to achieve possible optimization.
For Example: In C++, there are possibilities of short-circuiting at a time of evaluating && (AND) and || (OR) operators. At the time of evaluating && (AND) operator if the expression on the left-hand side of the operator gives a false result, then irrespective of the values of the right-hand side the boolean expression will always give a false as the final result. So, in this situation evaluation of the right-hand side is avoided by the compiler.
Similarly, in the case of the || (OR) operator when the left hand evaluates to true, the result of the expression will always be true irrespective of the value of the right-hand side of the operator.
3. ! (NOT) Operator: The ! (NOT) Operator in C is used to negate the boolean value used after it. It only requires a single boolean value as an expression.
Example:
The truth table for the || (AND) Operator is given below,
Now let’s try to use these logical operators with booleans in C using a simple example.Now let’s try to use these logical operators with booleans in C using a simple example.
In the above example, we have seen how various boolean operators like AND, OR, and NOT evaluate the boolean values.
# Boolean
Using the system header file stdbool.h allows you to use bool as a Boolean data type. true evaluates to 1 and false evaluates to 0 .
bool is just a nice spelling for the data type _Bool
(opens new window) . It has special rules when numbers or pointers are converted to it.
# Using #define
C of all versions, will effectively treat any integer value other than 0 as true for comparison operators and the integer value 0 as false . If you don’t have _Bool or bool as of C99 available, you could simulate a Boolean data type in C using #define macros, and you might still find such things in legacy code.
Don’t introduce this in new code since the definition of these macros might clash with modern uses of <stdbool.h> .
# Using the Intrinsic (built-in) Type _Bool
Added in the C standard version C99, _Bool is also a native C data type. It is capable of holding the values 0 (for false) and 1 (for true).
_Bool is an integer type but has special rules for conversions from other types. The result is analogous to the usage of other types in if expressions
- If X has an arithmetic type (is any kind of number), z becomes 0 if X == 0 . Otherwise z becomes 1 .
- If X has a pointer type, z becomes 0 if X is a null pointer and 1 otherwise.
To use nicer spellings bool , false and true you need to use <stdbool.h>
# Integers and pointers in Boolean expressions.
All integers or pointers can be used in an expression that is interpreted as "truth value".
The expression argc % 4 is evaluated and leads to one of the values 0 , 1 , 2 or 3 . The first, 0 is the only value that is "false" and brings execution into the else part. All other values are "true" and go into the if part.
Here the pointer A is evaluated and if it is a null pointer, an error is detected and the program exits.
Many people prefer to write something as A == NULL , instead, but if you have such pointer comparisons as part of other complicated expressions, things become quickly difficult to read.
For this to check, you’d have to scan a complicated code in the expression and be sure about operator preference.
is relatively easy to capture: if the pointer is valid we check if the first character is non-zero and then check if it is a letter.
# Defining a bool type using typedef
Considering that most debuggers are not aware of #define macros, but can check enum constants, it may be desirable to do something like this:
This allows compilers for historic versions of C to function, but remains forward compatible if the code is compiled with a modern C compiler.
For more information on typedef , see Typedef
# Remarks
To use the predefined type _Bool and the header <stdbool.h> , you must be using the C99/C11 versions of C.
To avoid compiler warnings and possibly errors, you should only use the typedef / define example if you’re using C89 and previous versions of the language.
bool in C
The bool in C is a fundamental data type in most that can hold one of two values: true or false. It is used to represent logical values and is commonly used in programming to control the flow of execution in decision-making statements such as if-else statements, while loops, and for loops. In this article, we will explore how to use the bool data type in C.
Boolean in C
In C, the bool data type is not a built-in data type. However, the C99 standard for C language supports bool variables. Boolean can store values as true-false, 0-1, or can be yes-no. It can be implemented in C using different methods as mentioned below:
boolean (bool or _Bool) datatype in C
C programming language (from C99) supports Boolean data type (bool) and internally, it was referred as _Bool as boolean was not a datatype in early versions of C. In C, boolean is known as bool data type. To use boolean, a header file stdbool.h must be included to use bool in C.
bool is an alias to _Bool to avoid breaking existing C code which might be using bool as an identifier. You can learn about _Bool here in detail.
Note if we do not include the above header file, then we need to replace bool with _Bool and the code will work as usually.
Standard logical operators AND (&&), OR(||) and NOT(!) can be used with the Boolean type in any combination.
In computer science, the Boolean data type is a data type that has one of two possible values, either TRUE or FALSE. Due to two possible values, it needs only 1 bit. In actual computing systems, the minimum amount of memory is set to a particular value (usually 8 bits) which is used (all bits as 0 or 1).
Memory
An object declared as type Bool is large enough to store the values 0 and 1.
The above code will give size 1 for bool, so generally bool store a 1 byte of memory. Note: it needs only 1 bit but takes 8 bits due to the structure of the computing system.
- true is denoted as 00000001
- false is denoted as 00000000
Declaration
To declare a variable as a boolean use:
Bool with Logical Operators
We can use logical operators with boolean.
Types of logical operators:
- && (AND): takes 2 booleans; returns true only if both operands are true else false
- || (OR): returns true if either or both of the operands are true else false
- ! (NOT): takes 1 operand; return true if operand is false and false if operand is true
Bool Array
How to convert a boolean to integer? (type casting)
A type cast is basically a conversion from one type to another.
An object declared as type Bool is large enough to store the values 0 and 1.
There’s no need to cast to bool for built-in types because that conversion is implicit. On converting to other integral types, a true bool will become 1 and a false bool will become 0.