Operators (Arithmetic, Logical, Relational, Bitwise, Assignment, Ternary, sizeof())

📖 Theory

Boxes full, now do something

The marks program stores three subject marks: 78, 65, 92. Storage was last lesson. Today the accountant work: total, percentage, and the question every student actually asks, did I pass?

Every one of those is an operator at work. Operators are the verbs of C, and like verbs in any language, two that look almost identical (= and ==) mean completely different things, and confusing them has crashed real payroll runs.

📊 At a glance

The operator families

📖 Theory

Arithmetic's two famous surprises

Surprise 1, integer division: with int boxes, 235 / 3 is 78, not 78.33. Two ints divide into an int; decimals are discarded (truncation again). Want the decimals? Make one side floating: 235 / 3.0 gives 78.33.

Surprise 2, the % operator: % is modulus, the REMAINDER after division: 7 % 2 is 1, 10 % 5 is 0. It has nothing to do with percentages, despite the symbol. (Odd/even tests, cyclic rolls, and half the exam's tricky questions run on %.)

⌨️ Practical

The marks program computes

#include <stdio.h>

int main() {
    int m1 = 78, m2 = 65, m3 = 92;
    int total = m1 + m2 + m3;
    float percentage = total / 3.0;   /* 3.0, not 3 */
    char result = (percentage >= 35) ? 'P' : 'F';

    printf("Total: %d\n", total);
    printf("Percentage: %f\n", percentage);
    printf("Result: %c\n", result);
    return 0;
}

This example runs in Gri-Learn on the web, where you can edit it and see the output.

💭 Think first

Read the ternary like a sentence

The line result = (percentage >= 35) ? 'P' : 'F'; is the ternary operator. Read it aloud as an English sentence first, then say what result holds for percentage 78.33.

🧩 Quiz

In C, what is the value of 7 % 2, and separately, of 7 / 2 (both ints)?

1. 7 % 2 is 1, and 7 / 2 is 3
2. 7 % 2 is 3.5, and 7 / 2 is 3.5
3. 7 % 2 is 3, and 7 / 2 is 1
4. 7 % 2 is 1, and 7 / 2 is 3.5

🧩 Quiz

A student writes if (marks = 100) intending to check for a perfect score. What actually happens?

1. marks is ASSIGNED 100, and the condition is always true
2. C compares marks with 100 as intended
3. The compiler always rejects it as an error
4. The condition is always false

⚠️ Watch out

The three mark-eaters

= vs == (assign vs compare, above). Integer division: total / 3 with ints silently drops decimals; write 3.0 or use float. Relational results: in C a comparison yields 1 or 0, not "true/false" words, so printf("%d", 5 > 3) prints 1, a favourite predict-the-output question. Bitwise operators exist (& | ^ << >>) and work on bits; at this stage exams want their NAMES, not mastery.

📖 Theory

sizeof: the measuring tape

sizeof(int) answers "how many bytes is this box?", typically 4, and sizeof(marks) measures a variable. It looks like a function but is an operator, exams ask exactly that. You will meet it again with arrays and pointers, where measuring boxes becomes daily work. Next lesson: the toolbox lines at the top of every program, #include and #define, finally explained.

✅ Summary

Key takeaways

• Operator families: arithmetic, relational, logical, assignment, ternary, bitwise, sizeof.
• Integer division truncates (7/2 is 3); % gives the remainder (7%2 is 1).
• = assigns, == asks; if (marks = 100) assigns and is always true.
• Relational and logical results are 1 (true) or 0 (false).
• Ternary: condition ? ifTrue : ifFalse, C's only three-operand operator.
• sizeof is an operator that reports a box's bytes.
• Memory hook: operators are C's verbs; = assigns, == asks.