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CHAP. 2]

2.6 ARITHMETIC OPERATORS Computers were invented to perform numerical calculations. Like most programming languages, C++ performs its numerical calculations by means of the five arithmetic operators +, , *, /, and %. EXAMPLE 2.4 Integer Arithmetic

This example illustrates how the arithmetic operators work. int main() { // tests operators +, -, *, /, and %: int m=54; int n=20; cout << "m = " << m << " and n = " << n << endl; cout << "m+n = " << m+n << endl; // 54+20 = 74 cout << "m-n = " << m-n << endl; // 54-20 = 34 cout << "m*n = " << m*n << endl; // 54*20 = 1080 cout << "m/n = " << m/n << endl; // 54/20 = 2 cout << "m%n = " << m%n << endl; // 54%20 = 14 } m = 54 and n = 20 m+n = 74 m-n = 34 m*n = 1080 m/n = 2 m%n = 14 Note that integer division results in another integer: 54/20 = 2, not 2.7.

The last two operators used in Example 2.4 are the division operator / and the modulus operator % (also called the remainder operator). The modulus operator results in the remainder from the division. Thus, 54%20 = 14 because 14 is the remainder after 54 is divided by 20. 2.7 THE INCREMENT AND DECREMENT OPERATORS The values of integral objects can be incremented and decremented with the ++ and -operators, respectively. Each of these operators has two versions: a pre version and a post version. The pre version performs the operation (either adding 1 or subtracting 1) on the object before the resulting value is used in its surrounding context. The post version performs the operation after the object s current value has been used. EXAMPLE 2.5 Applying the Pre-increment and Post-increment Operators

int main() { // shows the difference between m++ and ++m: int m, n; m = 44; n = ++m; // the pre-increment operator is applied to m cout << "m = " << m << ", n = " << n << endl;

m = 44; n = m++; // the post-increment operator is applied to m cout << "m = " << m << ", n = " << n << endl; } m = 45, n = 45 m = 45, n = 44

The line n = ++m; // the pre-increment operator is applied to m increments m to 45 and then assigns that value to n. So both variables have the same value 45 when the next output line executes. The line n = m++; // the post-increment operator is applied to m increments m to 45 only after it has assigned the value of m to n. So n has the value 44 when the next output line executes.

2.8 COMPOSITE ASSIGNMENT OPERATORS The standard assignment operator in C++ is the equals sign =. In addition to this operator, C++ also includes the following composite assignment operators: +=, -=, *=, /=, and %=. When applied to a variable on the left, each applies the indicated arithmetic operation to it using the value of the expression on the right. EXAMPLE 2.6 Applying Composite Arithmetic Assignment Operators

int main() { // tests arithmetic assignment operators: int n=22; cout << "n = " << n << endl; n += 9; // adds 9 to n cout << "After n += 9, n = " << n << endl; n -= 5; // subtracts 5 from n cout << "After n -= 5, n = " << n << endl; n *= 2; // multiplies n by 3 cout << "After n *= 2, n = " << n << endl; n /= 3; // divides n by 9 cout << "After n /= 3, n = " << n << endl; n %= 7; // reduces n to the remainder from dividing by 4 cout << "After n %= 7, n = " << n << endl; } n = 22 After n += 9, n = 31 After n -= 5, n = 26 After n *= 2, n = 52 After n /= 3, n = 17 After n %= 7, n = 3