Operators & Expressions

⚙️ C Language 🟢 Lesson 3 of 20 📅 2026 Edition

C provides a rich set of operators for performing calculations, comparisons, and logical decisions. Many will feel familiar if you've used other languages, but a few — especially the increment and compound assignment operators — are used far more heavily in C than elsewhere.

1Arithmetic Operators

C Language ▶ Run Code

int a = 10, b = 3;
printf("%d\n", a + b);   // 13
printf("%d\n", a - b);   // 7
printf("%d\n", a * b);   // 30
printf("%d\n", a / b);   // 3   (integer division truncates!)
printf("%d\n", a % b);   // 1   remainder

Note that dividing two int values always produces an int result, discarding any decimal part. To get a decimal answer, at least one operand must be a float or double.

2Relational and Logical Operators

C Language ▶ Run Code

int x = 5, y = 10;
printf("%d\n", x == y);        // 0 (false)
printf("%d\n", x != y);        // 1 (true)
printf("%d\n", x < y && y > 0);  // 1 (true) - both conditions true
printf("%d\n", x > y || y > 0);  // 1 (true) - at least one condition true

C has no true boolean type in its original form — comparisons simply evaluate to the integer 1 (true) or 0 (false), which you can store directly in an int.

3Increment, Decrement, and Compound Assignment

C Language ▶ Run Code

int count = 5;
count++;        // same as count = count + 1  (now 6)
count--;        // same as count = count - 1  (back to 5)
count += 10;    // same as count = count + 10 (now 15)
count *= 2;     // same as count = count * 2  (now 30)

These shortcuts appear constantly in C code, especially inside loops, so getting comfortable reading them quickly is essential.

4Pre-increment vs Post-increment

++count (pre-increment) increases the value before it's used in an expression. count++ (post-increment) uses the current value first, then increases it afterward:

C Language ▶ Run Code

int a = 5;
printf("%d\n", ++a);  // prints 6 (incremented first)

int b = 5;
printf("%d\n", b++);  // prints 5 (uses old value, then becomes 6)

⚠️ Common Mistake: Assuming Integer Division Gives a Decimal Result

7 / 2 in C evaluates to 3, not 3.5, because both operands are integers. To get a decimal result, cast at least one value: (float)7 / 2 correctly gives 3.5.

💻 Try It Yourself

Write a program that calculates both the integer quotient and the true decimal result of dividing two numbers, to see the difference clearly.

C Language ▶ Run Code

#include <stdio.h>

int main() {
    int a = 17, b = 5;
    printf("Integer division: %d\n", a / b);
    printf("Decimal division: %.2f\n", (float)a / b);
    return 0;
}

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