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Operators in C

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C language is rich in built-in operators and provides the following types of operators:

Arithmetic Operators
Relational Operators
Logical Operators
Bitwise Operators
Assignment Operators
Miscellaneous Operators

This chapter will逐一introduce arithmetic operators, relational operators, logical operators, bitwise operators, assignment operators, and other operators.

Arithmetic Operators

The following table shows all the arithmetic operators supported by the C language. Assume variable A holds 10 and variable B holds 20, then:

Operator	Description	Example
+	Adds two operands	A + B will give 30
-	Subtracts the second operand from the first	A - B will give -10
*	Multiplies both operands	A * B will give 200
/	Divides the numerator by the denominator	B / A will give 2
%	Modulus operator, remainder of the division	B % A will give 0
++	Increment operator, increases the integer value by one	A++ will give 11
--	Decrement operator, decreases the integer value by one	A-- will give 9

Example

Consider the following example to understand all the arithmetic operators available in C:

#include <stdio.h>

int main()
{
   int a = 21;
   int b = 10;
   int c;

   c = a + b;
   printf("Line 1 - Value of c is %d\n", c);
   c = a - b;
   printf("Line 2 - Value of c is %d\n", c);
   c = a * b;
   printf("Line 3 - Value of c is %d\n", c);
   c = a / b;
   printf("Line 4 - Value of c is %d\n", c);
   c = a % b;
   printf("Line 5 - Value of c is %d\n", c);
   c = a++;  // Assign then increment, c is 21, a is 22
   printf("Line 6 - Value of c is %d\n", c);
   c = a--;  // Assign then decrement, c is 22, a is 21
   printf("Line 7 - Value of c is %d\n", c);
}

When the above code is compiled and executed, it produces the following result:

Line 1 - Value of c is 31
Line 2 - Value of c is 11
Line 3 - Value of c is 210
Line 4 - Value of c is 2
Line 5 - Value of c is 1
Line 6 - Value of c is 21
Line 7 - Value of c is 22

The following example demonstrates the difference between a++ and ++a:

#include <stdio.h>

int main()
{
   int c;
   int a = 10;
   c = a++; 
   printf("Post-increment:\n");
   printf("Line 1 - Value of c is %d\n", c);
   printf("Line 2 - Value of a is %d\n", a);
   a = 10;
   c = a--; 
   printf("Line 3 - Value of c is %d\n", c);
   printf("Line 4 - Value of a is %d\n", a);

   printf("Pre-increment:\n");
   a = 10;
   c = ++a; 
   printf("Line 5 - Value of c is %d\n", c);
   printf("Line 6 - Value of a is %d\n", a);
   a = 10;
   c = --a; 
   printf("Line 7 - Value of c is %d\n", c);
   printf("Line 8 - Value of a is %d\n", a);
}

The above program produces the following output:

Post-increment:
Line 1 - Value of c is 10
Line 2 - Value of a is 11
Line 3 - Value of c is 10
Line 4 - Value of a is 9
Pre-increment:
Line 5 - Value of c is 11
Line 6 - Value of a is 11
Line 7 - Value of c is 9
Line 8 - Value of a is 9

Relational Operators

The following table shows all the relational operators supported by C. Assume variable A holds 10 and variable B holds 20, then:

Operator	Description	Example
==	Checks if the values of two operands are equal, if yes then the condition becomes true.	(A == B) is false.
!=	Checks if the values of two operands are equal, if values are not equal then the condition becomes true.	(A != B) is true.
>	Checks if the value of the left operand is greater than the value of the right operand, if yes then the condition becomes true.	(A > B) is false.
<	Checks if the value of the left operand is less than the value of the right operand, if yes then the condition becomes true.	(A < B) is true.
>=	Checks if the value of the left operand is greater than or equal to the value of the right operand, if yes then the condition becomes true.	(A >= B) is false.
<=	Checks if the value of the left operand is less than or equal to the value of the right operand, if yes then the condition becomes true.	(A <= B) is true.

Example

Consider the following example to understand all the relational operators available in C:

#include <stdio.h>

int main()
{
   int a = 21;
   int b = 10;

   if( a == b )
   {
      printf("Line 1 - a is equal to b\n");
   }
   else
   {
      printf("Line 1 - a is not equal to b\n");
   }
   if ( a < b )
   {
      printf("Line 2 - a is less than b\n");
   }
   else
   {
      printf("Line 2 - a is not less than b\n");
   }
   if ( a > b )
   {
      printf("Line 3 - a is greater than b\n");
   }
   else
   {
      printf("Line 3 - a is not greater than b\n");
   }
   /* Change the values of a and b */
   a = 5;
   b = 20;
   if ( a <= b )
   {
      printf("Line 4 - a is either less than or equal to b\n");
   }
   if ( b >= a )
   {
      printf("Line 5 - b is either greater than or equal to a\n");
   }
}

When the above code is compiled and executed, it produces the following result:

Line 1 - a is not equal to b
Line 2 - a is not less than b
Line 3 - a is greater than b
Line 4 - a is either less than or equal to b
Line 5 - b is either greater than or equal to a

Logical Operators

The following table shows all the logical operators supported by C. Assume variable A holds 1 and variable B holds 0, then:

Operator	Description	Example
&&	Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.	(A && B) is false.
			Called Logical OR operator. If any of the two operands is non-zero, then the condition becomes true.	(A	B) is true.
!	Called Logical NOT operator. It is used to reverse the logical state of its operand. If a condition is true, then the Logical NOT operator will make it false.	!(A && B) is true.

Example

Consider the following example to understand all the logical operators available in C:

#include <stdio.h>

int main()
{
   int a = 5;
   int b = 20;
   int c;

   if ( a && b )
   {
      printf("Line 1 - Condition is true\n");
   }
   if ( a || b )
   {
      printf("Line 2 - Condition is true\n");
   }
   /* Change the values of a and b */
   a = 0;
   b = 10;
   if ( a && b )
   {
      printf("Line 3 - Condition is true\n");
   }
   else
   {
      printf("Line 3 - Condition is false\n");
   }
   if ( !(a && b) )
   {
      printf("Line 4 - Condition is true\n");
   }
}

When the above code is compiled and executed, it produces the following result:

Line 1 - Condition is true
Line 2 - Condition is true
Line 3 - Condition is false
Line 4 - Condition is true

Bitwise Operators

Bitwise operators work on bits and perform bit-by-bit operation. The truth tables for &, |, and ^ are as follows:

p	q	p & q	p	q
0	0	0	0	0
0	1	0	1	1
1	1	1	1	0
1	0	0	1	1

Assume A = 60 and B = 13 in binary format, they will be as follows:

A = 0011 1100

B = 0000 1101

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:

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

Example

Consider the following example to understand all the bitwise operators available in C:

#include <stdio.h>

int main()
{
   unsigned int a = 60;    /* 60 = 0011 1100 */  
   unsigned int b = 13;    /* 13 = 0000 1101 */
   int c = 0;           

   c = a & b;       /* 12 = 0000 1100 */ 
   printf("Line 1 - Value of c is %d\n", c );

   c = a | b;       /* 61 = 0011 1101 */
   printf("Line 2 - Value of c is %d\n", c );

   c = a ^ b;       /* 49 = 0011 0001 */
   printf("Line 3 - Value of c is %d\n", c );

   c = ~a;          /*-61 = 1100 0011 */
   printf("Line 4 - Value of c is %d\n", c );

   c = a << 2;     /* 240 = 1111 0000 */
   printf("Line 5 - Value of c is %d\n", c );

   c = a >> 2;     /* 15 = 0000 1111 */
   printf("Line 6 - Value of c is %d\n", c );
}

When the above code is compiled and executed, it produces the following result:

Line 1 - Value of c is 12
Line 2 - Value of c is 61
Line 3 - Value of c is 49
Line 4 - Value of c is -61
Line 5 - Value of c is 240
Line 6 - Value of c is 15

printf("Line 1 - The value of c is %d\n", c );

c = a | b;       /* 61 = 0011 1101 */
printf("Line 2 - The value of c is %d\n", c );

c = a ^ b;       /* 49 = 0011 0001 */
printf("Line 3 - The value of c is %d\n", c );

c = ~a;          /*-61 = 1100 0011 */
printf("Line 4 - The value of c is %d\n", c );

c = a << 2;     /* 240 = 1111 0000 */
printf("Line 5 - The value of c is %d\n", c );

c = a >> 2;     /* 15 = 0000 1111 */
printf("Line 6 - The value of c is %d\n", c );
}

When the above code is compiled and executed, it produces the following result:

Line 1 - The value of c is 12
Line 2 - The value of c is 61
Line 3 - The value of c is 49
Line 4 - The value of c is -61
Line 5 - The value of c is 240
Line 6 - The value of c is 15

Assignment Operators

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

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

Example

Consider the following example to understand the usage of assignment operators in C:

#include <stdio.h>

int main()
{
   int a = 21;
   int c ;

   c =  a;
   printf("Line 1 - =  Operator Example, Value of c = %d\n", c );

   c +=  a;
   printf("Line 2 - += Operator Example, Value of c = %d\n", c );

   c -=  a;
   printf("Line 3 - -= Operator Example, Value of c = %d\n", c );

   c *=  a;
   printf("Line 4 - *= Operator Example, Value of c = %d\n", c );

   c /=  a;
   printf("Line 5 - /= Operator Example, Value of c = %d\n", c );

   c  = 200;
   c %=  a;
   printf("Line 6 - %= Operator Example, Value of c = %d\n", c );

   c <<=  2;
   printf("Line 7 - <<= Operator Example, Value of c = %d\n", c );

   c >>=  2;
   printf("Line 8 - >>= Operator Example, Value of c = %d\n", c );

   c &=  2;
   printf("Line 9 - &= Operator Example, Value of c = %d\n", c );

   c ^=  2;
   printf("Line 10 - ^= Operator Example, Value of c = %d\n", c );

   c |=  2;
   printf("Line 11 - |= Operator Example, Value of c = %d\n", c );

}

When the above code is compiled and executed, it produces the following result:

Line 1 - =  Operator Example, Value of c = 21
Line 2 - += Operator Example, Value of c = 42
Line 3 - -= Operator Example, Value of c = 21
Line 4 - *= Operator Example, Value of c = 441
Line 5 - /= Operator Example, Value of c = 21
Line 6 - %= Operator Example, Value of c = 11
Line 7 - <<= Operator Example, Value of c = 44
Line 8 - >>= Operator Example, Value of c = 11
Line 9 - &= Operator Example, Value of c = 2
Line 10 - ^= Operator Example, Value of c = 0
Line 11 - |= Operator Example, Value of c = 2

Miscellaneous Operators ↦ sizeof & ternary

The following table lists some other important operators including sizeof and ? : available in C.

Operator	Description	Example
sizeof()	Returns the size of a variable.	sizeof(a) will return 4, where a is an integer.
&	Returns the address of a variable.	&a; will give the actual address of the variable.
*	Pointer to a variable.	*a; will point to a variable.
? :	Conditional Expression	If Condition is true ? Then value X : Otherwise value Y

Example

Consider the following example to understand the usage of miscellaneous operators in C:

#include <stdio.h>

int main()
{
   int a = 4;
   short b;
   double c;
   int* ptr;

   /* sizeof operator example */
   printf("Line 1 - Size of variable a = %lu\n", sizeof(a) );
   printf("Line 2 - Size of variable b = %lu\n", sizeof(b) );
   printf("Line 3 - Size of variable c = %lu\n", sizeof(c) );

   /* & and * operators example */
   ptr = &a;    /* 'ptr' now contains the address of 'a' */
   printf("a 的值是 %d\n", a);
   printf("*ptr 是 %d\n", *ptr);

   /* Ternary operator example */
   a = 10;
   b = (a == 1) ? 20: 30;
   printf( "b 的值是 %d\n", b );

   b = (a == 10) ? 20: 30;
   printf( "b 的值是 %d\n", b );
}

When the above code is compiled and executed, it produces the following result:

Line 1 - Size of variable a = 4
Line 2 - Size of variable b = 2
Line 3 - Size of variable c = 8
a 的值是 4
*ptr 是 4
b 的值是 30
b 的值是 20

Operator Precedence in C

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

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

The following table lists the precedence and associativity of operators. Operators with higher precedence appear at the top of the table, and those with lower precedence appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

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

Example

Consider the following example to understand the operator precedence in C:

#include <stdio.h>

main()
{
   int a = 20;
   int b = 10;
   int c = 15;
   int d = 5;
   int e;

   e = (a + b) * c / d;      // ( 30 * 15 ) / 5
   printf("(a + b) * c / d 的值是 %d\n",  e );

   e = ((a + b) * c) / d;    // (30 * 15 ) / 5
   printf("((a + b) * c) / d 的值是 %d\n" ,  e );

   e = (a + b) * (c / d);   // (30) * (15/5)
   printf("(a + b) * (c / d) 的值是 %d\n",  e );

   e = a + (b * c) / d;     //  20 + (150/5)
   printf("a + (b * c) / d 的值是 %d\n" ,  e );

   return 0;
}

When the above code is compiled and executed, it produces the following result:

(a + b) * c / d 的值是 90
((a + b) * c) / d 的值是 90
(a + b) * (c / d) 的值是 90
a + (b * c) / d 的值是 50

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