AM FL Y in Java

Drawer PDF 417 in Java AM FL Y

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2 covers expressions thoroughly However, a few special points are mentioned here Remember, an expression statement is simply a valid expression followed by a semicolon, as in

func(); a = b+c; b+f(); ; /* /* /* /* a function call */ an assignment statement */ a valid, but strange statement */ an empty statement */

The first expression statement executes a function call The second is an assignment The third expression, though strange, is still evaluated by the compiler because the function f( ) may perform some necessary task The final example shows that a statement can be empty (sometimes called a null statement)

Block statements are groups of related statements that are treated as a unit The statements that make up a block are logically bound together Block statements are also called compound statements A block begins with a { and terminates by its matching } Block statements are most commonly used to create a multistatement target for some other statement, such as if

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unctions are the building blocks of C and C++ and the place where all program activity occurs This chapter examines their features, including function arguments, return values, prototypes, and recursion

The general form of a function is ret-type function_name(parameter list) { body of the function } The ret-type specifies the type of data that the function returns A function can return any type of data except an array The parameter list is a comma-separated list of variable names and their associated types The parameters receive the values of the arguments when the function is called A function can be without parameters, in which case the parameter list is empty An empty parameter list can be explicitly specified by placing the keyword void inside the parentheses

The return statement has two important uses First, it causes an immediate exit from the function That is, it causes program execution to return to the calling code Second, it can be used to return a value The following section examines how the return statement is applied

A function terminates execution and returns to the caller in one of two ways The first is when the last statement in the function has executed and, conceptually, the function s ending curly brace (}) is encountered (Of course, the curly brace isn t actually present in the object code, but you can think of it in this way) For example, this function takes an address to a string as a parameter and displays the string backward:

void pr_reverse(char *s) { register int t; for(t=strlen(s)-1; t >= 0; t--) printf("%c", s[t]); }

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Once the string has been displayed, there is nothing left for pr_reverse( ) to do, so it returns to the place from which it was called Actually, not many functions use this default method of terminating their execution Most functions rely on the return statement to stop execution either because a value must be returned or to make a function s code simpler and more efficient A function may contain several return statements For example, the find_substr( ) function, shown next, returns either the starting position of a substring within a string or 1 if no match is found It uses two return statements to simplify the coding:

int find_substr(char *s1, char *s2) { register int t; char *p, *p2; for(t=0; s1[t]; t++) { p = &s1[t]; p2 = s2; while(*p2 && *p2==*p) { p++; p2++; } if(!*p2) return t; /* substring was found */ } return -1; /* substring not found */ }

All functions, except those of type void, return a value This value is specified by the return statement In C89, if a non-void function executes a return statement that does not include a value, then a garbage value is returned In C++ (and C99), a non-void function must use a return statement that returns a value As long as a function is not declared as void, you can use it as an operand in an expression Therefore, each of the following expressions is valid:

x = power(y); if(max(x, y) > 100) printf("greater"); for(ch=getchar(); isdigit(ch); ) ;