Operator, Operand and Expression

An operator is a symbol that tells the compiler to perform one specific operation and produce a value. An operand is the piece of data the operator works on. An operand can be a variable, a constant, or even another expression. When operands and operators are joined together in a legal way, the result is an expression, and every expression evaluates to a value.

Take the line total = price * qty. Here price and qty are operands of the multiplication operator, and the multiplication result becomes the right-hand operand of the assignment operator. One line, two operators, one expression tree.

Unary and Binary Operators

Operators are classified by how many operands they need. A unary operator works on exactly one operand (-y). A binary operator needs two (x + y). C also has one ternary operator (?:) that takes three, which you will meet in the conditional operator lecture.

The Ten Operator Families in C

C packs a large number of operators, grouped into families. This free C programming course covers all of them across Chapter 4 and Chapter 5.

Arithmetic Operators in C

Arithmetic operators perform numeric calculations. They come in two flavours: unary arithmetic operators and binary arithmetic operators.

Unary Arithmetic Operators

There are two: unary plus (+x) and unary minus (-y). Unary minus flips the sign of its operand. Unary plus returns the value unchanged; it exists mostly for symmetry and readability.

Binary Arithmetic Operators

Modulus and the Missing Exponent Operator

The modulus operator % works only on integer operands. Applying it to a float or double is rejected by the compiler. If you need a floating-point remainder, the standard library provides fmod() in <math.h>.

C also has no exponent operator. The caret ^ is bitwise XOR, not power. To raise a number to a power, call pow() from <math.h>, which takes and returns double. On Linux, link the math library with -lm.

Hands-On Examples (Free C Programming Course Labs)

Save each program in its own file and compile with gcc -Wall -Wextra -std=c11 file.c -o out. Add -lm where math.h functions are used.

Example 1: Unary Plus and Minus

/* cp4_1_ex1.c - unary operators */
#include <stdio.h>

int main(void)
{
    int temp = 25;
    int flipped = -temp;
    int same = +temp;

    printf("temp=%d flipped=%d same=%d\n", temp, flipped, same);
    printf("-(-temp) = %d\n", -(-temp));
    return 0;
}

Expected output:

temp=25 flipped=-25 same=25
-(-temp) = 25

Notice that temp itself never changes. Unary minus produces a new value; it does not modify the variable.

Example 2: All Five Binary Operators

/* cp4_1_ex2.c - binary arithmetic */
#include <stdio.h>

int main(void)
{
    int a = 29, b = 6;

    printf("a + b = %d\n", a + b);
    printf("a - b = %d\n", a - b);
    printf("a * b = %d\n", a * b);
    printf("a / b = %d\n", a / b);
    printf("a %% b = %d\n", a % b);
    return 0;
}

a + b = 35
a - b = 23
a * b = 174
a / b = 4
a % b = 5

To print a literal percent sign with printf you must write %%. Check the relationship: 4 × 6 + 5 = 29.

Example 3: Power with pow()

/* cp4_1_ex3.c - exponentiation */
#include <stdio.h>
#include <math.h>

int main(void)
{
    double result = pow(2.0, 10.0);
    printf("2 to the power 10 = %.0f\n", result);
    return 0;
}

$ gcc cp4_1_ex3.c -o ex3 -lm
$ ./ex3
2 to the power 10 = 1024

Example 4: The Compiler Rejects % on Floats

/* cp4_1_ex4.c - this one does NOT compile */
#include <stdio.h>

int main(void)
{
    double x = 7.5;
    printf("%f\n", x % 2);
    return 0;
}

$ gcc cp4_1_ex4.c -o ex4
cp4_1_ex4.c: In function 'main':
cp4_1_ex4.c:6:24: error: invalid operands to binary % (have 'double' and 'int')

Reading compiler errors is a core skill. The message names the operator and the exact operand types it refused.

Real-World Uses of Arithmetic Operators

• Embedded firmware: converting sensor counts to physical units, computing timer reload values, scaling PWM duty cycles.
• Linux system programs: computing buffer sizes, offsets and page counts.
• Everyday software: billing totals, tax, discounts, unit conversions.

Common Mistakes and Troubleshooting

Best Practices

• Use parentheses to make intent obvious, even where precedence would give the same answer.
• Prefer int main(void) and always compile with -Wall -Wextra.
• Never let a divisor reach zero; validate input before dividing.
• Keep one operation per line while learning, so you can print and inspect intermediate values.
• Performance note: on most embedded cores multiplication is cheap but division and modulus can be slow, especially on small microcontrollers with no hardware divider.

Conclusion

Operators are the verbs of the C language. You now know the vocabulary, the ten operator families, and the arithmetic operators with their restrictions. The next lecture of this free C programming course digs into integer arithmetic, where division and modulus behave in ways that surprise most beginners.

Quick Quiz

1. How many operands does the unary minus operator need?
   Show answer

   One.
2. What is the value of 14 % 5?
   Show answer

   4.
3. Which header declares pow()?
   Show answer

   math.h.
4. Is 7.0 % 2 valid in C?
   Show answer

   No. The compiler gives an invalid operands error.
5. What does 8 - -2 evaluate to?
   Show answer

   10.

Interview Questions

1. Define operator, operand and expression with an example.
2. What is the difference between unary minus and binary subtraction?
3. Why can’t you use % with floating-point numbers, and what is the alternative?
4. Does 2 ^ 3 give 8 in C? Explain.
5. Why is division considered expensive on small microcontrollers?

Frequently Asked Questions