Operators, Expressions, Precedence, Associativity, and Type Conversion in C

C provides a rich set of operators for arithmetic, comparison, logic, and more. But operators become genuinely useful only once you understand how they combine into expressions, and crucially, in what order they’re evaluated when several appear together. This is Post 4 of the Unit I series.

Categories of Operators

1. Arithmetic Operators

+   addition
-   subtraction
*   multiplication
/   division
%   modulus (remainder) — only works on integers

2. Relational Operators

==  equal to
!=  not equal to
>   greater than
<   less than
>=  greater than or equal to
<=  less than or equal to

3. Logical Operators

&&  logical AND
||  logical OR
!   logical NOT

4. Assignment Operators

=   assign
+=  add and assign   (a += 5  is short for  a = a + 5)
-=  subtract and assign
*=  multiply and assign
/=  divide and assign
%=  modulus and assign

5. Increment/Decrement Operators

++  increment by 1   (can be prefix ++a or postfix a++)
--  decrement by 1

Example: Prefix vs. Postfix

#include <stdio.h>

int main() {
    int a = 5, b = 5;

    printf("Postfix: %d\n", a++);  // prints 5 (uses value FIRST, then increments)
    printf("After postfix, a = %d\n", a);  // now 6

    printf("Prefix: %d\n", ++b);   // increments FIRST, then prints 6
    printf("After prefix, b = %d\n", b);

    return 0;
}

Sample Output

Postfix: 5
After postfix, a = 6
Prefix: 6
After prefix, b = 6

Expressions

An expression is any valid combination of operators, constants, and variables that evaluates to a single value.

a + b * c        // an expression
(x > 0) && (y > 0)  // an expression that evaluates to true/false (1 or 0 in C)

Precedence and Associativity

When an expression has multiple operators, C needs rules to decide which operation happens first.

• Precedence determines which operator binds “tighter” — e.g. * and / have higher precedence than + and -, so they’re evaluated first, just like in ordinary arithmetic (BODMAS/PEMDAS).
• Associativity determines the order of evaluation when operators of the same precedence appear together — left-to-right or right-to-left, depending on the operator.

A Simplified Precedence Table (Highest to Lowest)

Worked Example

int result = 10 + 20 * 3 - 4 / 2;

Step by step:

1. 20 * 3 = 60      (* has higher precedence than + and -)
2. 4 / 2 = 2         (/ also has higher precedence)
3. 10 + 60 = 70       (now left-to-right for + and -)
4. 70 - 2 = 68
   result = 68

Expression Evaluation with Mixed Types

#include <stdio.h>

int main() {
    int a = 7, b = 2;
    float c = 7.0, d = 2.0;

    printf("int / int    = %d\n", a / b);       // 3  (integer division truncates)
    printf("float / float = %.2f\n", c / d);     // 3.50
    printf("int / float  = %.2f\n", a / d);      // 3.50 (a is promoted to float)
    printf("mod (int only) = %d\n", a % b);      // 1

    return 0;
}

Sample Output

int / int    = 3
float / float = 3.50
int / float  = 3.50
mod (int only) = 1

Type Conversion

Type conversion happens in two ways:

• Implicit conversion (also called “type promotion”) — the compiler automatically converts one operand’s type to match the other, following C’s promotion rules (in general: char → int → float → double, promoting toward the “wider” type). This is what happened with a / d above — a (int) was implicitly promoted to float because d is a float.
• Explicit conversion (type casting) — you manually force a conversion using (type):

  float avg = (float) totalMarks / numSubjects;

Summary

• C has arithmetic, relational, logical, assignment, and increment/decrement operators.
• Precedence decides which operator is applied first; associativity breaks ties between operators of equal precedence.
• Prefix (++a) increments before using the value; postfix (a++) uses the value before incrementing.
• Implicit conversion happens automatically per C’s promotion rules; explicit conversion (casting) is done manually with (type).
• Integer division truncates — cast an operand to float/double before the division if you need a fractional result.

Further Reading

• Operator Precedence and Associativity in C Programming (video embedded above)
• GeeksforGeeks: Operator Precedence and Associativity in C

Next in this series: decision making with if, if-else, and switch statements.