Sams Teach Yourself C in 21 Days

The Pieces of a C Program: Statements, Expressions, and Operators 69

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the hours, line 23 uses the modulus operator to divide the hours and keep the remaining

minutes. Line 24 carries out a similar calculation for determining the number of seconds

that are left. Lines 26 and 27 are similar to what you have seen before. They take the val-

ues that have been calculated in the expressions and display them. Line 29 finishes the

program by returning 0 to the operating system before exiting.

Operator Precedence and Parentheses ............................................................

In an expression that contains more than one operator, what is the order in which opera-

tions are performed? The importance of this question is illustrated by the following

assignment statement:

x = 4 + 5 * 3;

Performing the addition first results in the following, and xis assigned the value 27 :

x = 9 * 3;

In contrast, if the multiplication is performed first, you have the following, and xis

assigned the value 19 :

x = 4 + 15;

Clearly, some rules are needed about the order in which operations are performed. This

order, called operator precedence,is strictly spelled out in C. Each operator has a spe-

cific precedence. When an expression is evaluated, operators with higher precedence are

performed first. Table 4.3 lists the precedence of C’s mathematical operators. Number 1

is the highest precedence and thus is evaluated first.

TABLE4.3 The precedence of C’s mathematical operators

Operators Relative Precedence

++ -- 1

* / % 2

+ - 3

Looking at Table 4.3, you can see that in any C expression, operations are performed in

the following order:

• Unary increment and decrement


• Multiplication, division, and modulus


• Addition and subtraction

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