Fundamentals of C Language Programming: Operators

1. Overview of Operators

Operators are symbols used in the C language to perform various operations, and they are the basic elements that make up expressions. C provides a rich variety of operator types that can perform arithmetic operations, relational comparisons, logical evaluations, bit manipulations, and more. Mastering the use of operators is an important foundation for learning C programming.

2. Classification of Operators

1. Arithmetic Operators

Arithmetic operators are used to perform basic mathematical operations:

Operator	Description	Example
+	Addition	a + b
–	Subtraction	a – b
*	Multiplication	a * b
/	Division	a / b
%	Modulus (Remainder)	a % b
++	Increment	a++ or ++a
—	Decrement	a– or –a

#include <stdio.h>
int main() {
    int a = 10, b = 3;
    printf("a + b = %d\n", a + b);  // 13
    printf("a - b = %d\n", a - b);  // 7
    printf("a * b = %d\n", a * b);  // 30
    printf("a / b = %d\n", a / b);  // 3 (integer division)
    printf("a %% b = %d\n", a % b); // 1
    int c = 5;
    printf("c++ = %d\n", c++); // Use c's value 5, then increment
    printf("++c = %d\n", ++c); // Increment to 7, then use
    return 0;
}

Output:

int a = 5, b = 2; float result = a / b;  // Note: integer division, result is 2.0 not 2.5

float f = 10.5; int mod = f % 3;  // Error: % operator cannot be used with floating-point numbers, only with integers

int i = 5; printf("%d", i++ + ++i);  // Undefined behavior, results may vary across compilers

Notes:

• Avoid using increment/decrement on the same variable multiple times in the same expression

• Clearly distinguish between prefix (++i) and postfix (i++) forms

2. Relational Operators

Relational operators are used to compare the size relationship between two values, returning 1 (true) or 0 (false):

Operator	Description	Example
==	Equal to	a == b
!=	Not equal to	a != b
>	Greater than	a > b
<	Less than	a < b
>=	Greater than or equal to	a >= b
<=	Less than or equal to	a <= b

#include <stdio.h>
int main() {
    int x = 5, y = 10;
    printf("x == y: %d\n", x == y); // 0
    printf("x != y: %d\n", x != y); // 1
    printf("x > y: %d\n", x > y);   // 0
    printf("x < y: %d\n", x < y);   // 1
    return 0;
}

Running result:

Notes:

• Use == for equality comparison, not =

3. Logical Operators

Logical operators are used to combine multiple conditions:

Operator	Description	Example
&&	Logical AND	a && b
||	Logical OR	a || b
!	Logical NOT	!a

#include <stdio.h>
int main() {
    int a = 5;  // 0101
    int b = 3;  // 0011
    // Logical operators
    printf("Logical AND: %d &amp;&amp; %d = %d\n", a, b, a &amp;&amp; b);  // 1
    printf("Logical OR: %d || %d = %d\n", a, b, a || b);  // 1
    printf("Logical NOT: !a = %d  !b = %d\n", !a,!b);  // 0  0
    return 0;
}

Output result:

Notes:

• && is used for boolean logic evaluation

• & is used for bitwise operations

4. Assignment Operators

Assignment operators are used to assign values to variables:

Operator	Description	Equivalent to
=	Simple assignment	a = b
+=	Add and assign	a += b → a = a + b
-=	Subtract and assign	a -= b → a = a – b
*=	Multiply and assign	a *= b → a = a * b
/=	Divide and assign	a /= b → a = a / b
%=	Modulus and assign	a %= b → a = a % b

#include <stdio.h>
int main() {
    int a = 10;
    a += 5;  // a = 15
    a -= 3;  // a = 12
    a *= 2;  // a = 24
    a /= 4;  // a = 6
    a %= 5;  // a = 1
    printf("Final value of a: %d\n", a);
    return 0;
}

Output result:

5. Bitwise Operators (Advanced)

Bitwise operators directly manipulate the binary bits of data:

Operator	Description	Example
&	Bitwise AND	a & b
|	Bitwise OR	a | b
^	Bitwise XOR	a ^ b
~	Bitwise NOT	~a
<<	Left shift	a << n
>>	Right shift	a >> n

#include <stdio.h>
int main() {
    unsigned char a = 5;  // Binary representation: 00000101
    unsigned char b = 3;  // Binary representation: 00000011
    printf("a &amp; b = %d\n", a &amp; b);  // 00000001 → 1
    printf("a | b = %d\n", a | b);  // 00000111 → 7
    printf("a ^ b = %d\n", a ^ b);  // 00000110 → 6
    printf("~a = %d\n", ~a &amp; 0xFF); // 11111010 → 250
    printf("a &lt;&lt; 1 = %d\n", a &lt;&lt; 1); // 00001010 → 10
    printf("a &gt;&gt; 1 = %d\n", a &gt;&gt; 1); // 00000010 → 2
    return 0;
}

Output result:

3. Operator Precedence

When an expression contains multiple operators, C determines the order of operations based on operator precedence and associativity:

Precedence	Operator	Precedence	Operator	Precedence	Operator
1	<span>() Parentheses</span>	6	==, !=	11	||
2	*, /, %	7	&	12	<span>?:</span> (Ternary operator)
3	+, –	8	^	13
4	<<, >>	9	|	14
5	<, <=, >, >=	10	&&	15

4. Special Operators

1. Conditional Operator (Ternary Operator)

Syntax:

<span><span>condition ? expression1 : expression2</span></span>

int a = 10, b = 20; int max = (a > b) ? a : b;  // max = 20

2. sizeof Operator

Returns the size (in bytes) of a variable or type:

printf("Size of int: %zu\n", sizeof(int));  // Usually 4
printf("Size of a: %zu\n", sizeof(a));     // Depends on the type of a

Notes:

• The multiplication (*) operator has higher precedence than addition (+)

• Use parentheses to clarify precedence when uncertain