1.4 Expressions and Operators

An expression combines values, variables, and operators. Programs use expressions to calculate, compare, and update data.

Arithmetic operators

C++ supports common addition, subtraction, multiplication, and division, plus the modulo operation.

• +, -, *: add, subtract, multiply
• /: division
• %: modulo (remainder)

When two integers are divided, C++ performs integer division and truncates the fractional part.

std::cout << 22 / 3 << std::endl;   // 7
std::cout << 22 % 3 << std::endl;   // 1

To get a decimal result, at least one operand must be floating point.

std::cout << 22 / 3.0 << std::endl;   // 7.33333

Reversing a three-digit integer

Integer division and modulo are often used together to split an integer into digits.

int num = 520;
int a = num / 100;
int b = num / 10 % 10;
int c = num % 10;
std::cout << c * 100 + b * 10 + a << std::endl;

Output:

25

The result is displayed as 25 because the reversed number is 025, and leading zeros are not shown when printing an integer.

Compound operators

Compound assignment operators make variable updates shorter.

• a += b means a = a + b
• a -= b means a = a - b
• a *= b means a = a * b
• a /= b means a = a / b
• a %= b means a = a % b

Increment and decrement

C++ also provides the increment operator ++ and decrement operator --, which add 1 or subtract 1 from a variable. They are very common in loop counters.

int i = 5;
i++;   // i becomes 6
i--;   // i becomes 5

i++ is equivalent to i = i + 1, and i-- is equivalent to i = i - 1.