Cprogramming 简明教程

a + b

a > b

a >= 50 && b >= 50

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A = 1100 0011

The following table lists the bitwise operators supported by C. Assume variable 'A' holds 60 and variable 'B' holds 13, then −

link:../cprogramming/c_bitwise_operators.html[Show Examples]
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|===

|Operator|Description|Example
|&|Binary AND Operator copies a bit to the result if it exists in both operands.|(A & B) = 12, i.e., 0000 1100
|||Binary OR Operator copies a bit if it exists in either operand.|(A | B) = 61, i.e., 0011 1101
|^|Binary XOR Operator copies the bit if it is set in one operand but not both.|(A ^ B) = 49, i.e., 0011 0001
|~|Binary One's Complement Operator is unary and has the effect of 'flipping' bits.|(~A ) = ~(60), i.e,. -0111101
|<<|Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.|A << 2 = 240 i.e., 1111 0000
|>>|Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.|A >> 2 = 15 i.e., 0000 1111
|===


=== Assignment Operators

As the name suggests, an assignment operator "assigns" or sets a value to a named variable in C. These operators are used to assign values to variables. The "=" symbol is defined as assignment operator in C, however it is not to be confused with its usage in mathematics.

The following table lists the assignment operators supported by the C language −

link:../cprogramming/c_assignment_operators.html[Show Examples]
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|Operator|Description|Example
|=|Simple assignment operator. Assigns values from right side operands to left side operand|C = A + B will assign the value of A + B to C
|+=|Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.|C += A is equivalent to C = C + A
|-=|Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.|C -= A is equivalent to C = C - A
|*=|Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.|C *= A is equivalent to C = C * A
|/=|Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.|C /= A is equivalent to C = C / A
|%=|Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.|C %= A is equivalent to C = C % A
|<<=|Left shift AND assignment operator.|C <<= 2 is same as C = C << 2
|>>=|Right shift AND assignment operator.|C >>= 2 is same as C = C >> 2
|&=|Bitwise AND assignment operator.|C &= 2 is same as C = C & 2
|^=|Bitwise exclusive OR and assignment operator.|C ^= 2 is same as C = C ^ 2
||=|Bitwise inclusive OR and assignment operator.|C |= 2 is same as C = C | 2
|===

Hence, the expression "a = 5" assigns 5 to the variable "a", but "5 = a" is an invalid expression in C.

The "=" operator, combined with the other arithmetic, relational and bitwise operators form augmented assignment operators. For example, the += operator is used as add and assign operator. The most common assignment operators are =, +=, -=, *=, /=, %=, &=, |=, and ^=.


=== Misc Operators ↦ sizeof & ternary

Besides the operators discussed above, there are a few other important operators including *sizeof* and *? :* supported by the C Language.

link:../cprogramming/c_sizeof_operator.html[Show Examples]
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|Operator|Description|Example
|sizeof()|Returns the size of a variable.|sizeof(a), where a is integer, will return 4.
|&|Returns the address of a variable.|&a; returns the actual address of the variable.
|*|Pointer to a variable.|*a;
|? :|Conditional Expression.|If Condition is true ? then value X : otherwise value Y
|===


=== Operators Precedence in C

Operator precedence determines the grouping of terms in an expression and decides how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has a higher precedence than the addition operator.

For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has a higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

link:../cprogramming/c_operators_precedence.html[Show Examples]
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|Category|Operator|Associativity
|Postfix|() [] -> . ++ - -|Left to right
|Unary|+ - ! ~ ++ - - (type)* & sizeof|Right to left
|Multiplicative|* / %|Left to right
|Additive|+ -|Left to right
|Shift|<< >>|Left to right
|Relational|< <= > >=|Left to right
|Equality|== !=|Left to right
|Bitwise AND|&|Left to right
|Bitwise XOR|^|Left to right
|Bitwise OR|||Left to right
|Logical AND|&&|Left to right
|Logical OR||||Left to right
|Conditional|?:|Right to left
|Assignment|= += -= *= /= %=>>= <<= &= ^= |=|Right to left
|Comma|,|Left to right
|===


=== Other Operators in C

Apart from the above, there are a few other operators in C that are not classified into any of the above categories. For example, the increment and decrement operators (++ and --) are unary in nature and can appear as a prefix or postfix to the operand.

The operators that work with the address of memory location such as the address-of operator (&) and the dereference operator (*). The sizeof operator (sizeof) appears to be a keyword but really an operator.

C also has the type cast operator (()) that forces the type of an operand to be changed. C also uses the dot (.) and the arrow (->) symbols as operators when dealing with derived link:../cprogramming/c_data_types.html[data types] such as link:../cprogramming/c_structures.html[struct] and link:../cprogramming/c_unions.html[union].

The C99 version of C introduced a few additional operators such as auto, decltype.

A single expression in C may have multiple operators of different type. The link:../compile_c_online.php[C compiler] evaluates its value based on the operator precedence and associativity of operators. For example, in the following expression −

[source, c]

The multiplication operand takes precedence over the addition operator.

We shall understand these properties with examples in a subsequent chapter.

Many other programming languages, which are called C-family languages (such as link:../cplusplus/index.html[C++], link:../csharp/index.html[C#], link:../java/index.html[Java], link:../perl/index.html[Perl] and link:../php/index.html[PHP]) have an operator nomenclature that is similar to C.