UNIX — универсальная среда программирования - Керниган Брайан Уилсон
lfCW n l.
fBTable 3:fP Built-in Constants
.sp .5
DEG 57.29577951308232087680 @180/ [email protected], degrees per radian
E 2.71828182845904523536 @[email protected], base of natural logarithms
GAMMA 0.57721566490153286060 @[email protected], Euler-Mascheroni constant
PHI 1.61803398874989484820 @( sqrt 5 +1)/[email protected], the golden ratio
PI 3.14159265358979323846 @[email protected], circular transcendental number
.ТЕ
.ix table~of [hoc] constants
.NH
Statements and Control Flow
.PP
.I Hoc
statements have the following grammar:
.DS
.I
stmt: expr
| variable = expr
| procedure ( arglist )
| while ( expr ) stmt
| if ( expr ) stmt
| if ( expr ) stmt else stmt
| { stmtlist }
| print expr-list
| return optional-expr
stmtlist: fR(nothing)fI
| stmlist stmt
.R
.DE
An assignment is parsed by default as a statement rather than
an expression, so assignments typed interactively
do not print their value.
.PP
Note that semicolons are not special to
.ix [hoc] input~format
@[email protected]: statements are terminated by newlines.
This causes some peculiar behavior.
The following are legal
.IT if
statements:
.DS
.ft CW
if (x < 0) print(y) else print(z)
if (x < 0) {
print(y)
} else {
print(z)
}
.ft
.DE
In the second example, the braces are mandatory:
the newline after the
.I if
would terminate the statement and produce a syntax error were
the brace omitted.
.PP
The syntax and semantics of @[email protected]
control flow facilities are basically the same as in C.
The
.I while
and
.I if
statements are just as in C, except there are no @[email protected] or
@[email protected] statements.
.NH
Input and Output: @[email protected] and @[email protected]
.PP
.ix [hoc] [read]~statement
.ix [hoc] [print]~statement
The input function @[email protected], like the other built-ins,
takes a single argument. Unlike the built-ins, though, the argument
is not ал expression: it is the name of a variable.
The next number (as defined above) is read from the standard input
and assigned to the named variable.
The return value of @[email protected] is 1 (true) if a value was read, and 0 (false)
if @[email protected] encountered end of file or an error.
.PP
Output is generated with the ©print© statement.
The arguments to @[email protected] are a comma-separated list of expressions
and strings in double quotes, as in C.
Newlines must be supplied;
they are never provided automatically by @[email protected]
.PP
Note that @[email protected] is a special built-in function, and therefore takes
a single parenthesized argument, while @[email protected] is a statement that takes
a comma-separated, unparenthesized list:
.DS
.ft CW
while (read(x)) {
print "value is ", x, "n"
}
.ft
.DE
.NH
Functions and Procedures
.PP
Functions and procedures are distinct in @[email protected],
although they are defined by the same mechanism.
This distinction is simply for run-time error checking:
it is an error for a procedure to return a value,
and for a function @[email protected] to return one.
.PP
The definition syntax is:
.ix [hoc] function~definition
.ix [hoc] procedure~definition
.DS
