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14. PRINT STATEMENT

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14.1General Description

The print-statement is designed for generation of tabular output in a consistent format.

The general syntactic form of the print-statement is


        PRINT item p item p ... p item

where each item is an expression, a tab-call, or null, and each punctuation mark p is either a comma or a semi-colon.

 

14.2 Syntax


            1. print-statement          = PRINT print-list?
            2. print-list               = (print-item? print-separator)* print-item ?
            3. print-item               = expression / tab-call
            4. tab-call                 = TAB left-parenthesis numeric-expression right-parenthesis
            5. print-separator          = comma / semicolon

14.3 Examples

PRINT X PRINT X; (Y+Z)/2 PRINT PRINT TAB(10); A$; "IS DONE."

14.4 Semantics

The execution of a print-statement generates a string of characters for transmission to an external device. This string of characters is determined by the successive evaluation of each print-item and print-separator in the print-list.

Numeric-expressions shall be evaluated to produce a string of characters consisting of a leading space if the number is positive or a leading minus-sign if the number is negative followed by the decimal representation of the absolute value of the number and a trailing space. The possible formats for the decimal representation of a number are the same as those described for numeric-constants in 6 and are used as follows.

Each implementation shall define two quantities, a significance- width d to control the number of significant decimal digits printed in numeric representations, and an exrad-width e to control the number of digits printed in the exrad component of a numeric representation. The value of d shall be at least six and the value of e shall be at least two.

Each number that can be represented exactly as an integer with d or fewer decimal digits is output using the implicit point unsealed representation.

All other numbers shall be output using either explicit point unsealed notation or explicit point scaled notation. Numbers which can be represented with d or fewer digits in the unsealed format no less accurately than they can be represented in the scaled format shall be output using the unsealed format. For example, if d = 6, then 10~(-6) is output as .000001 and l(T(-7) is output as l.E-7.

Numbers represented in the explicit point unsealed notation shall be output with up to d significant decimal digits and a full- stop; trailing zeroes in the fractional part may be omitted. A number with magnitude less than 1 shall be represented with no digits to the left of the full-stop. This form requires up to d+3 characters counting the sign, the full-stop and the trailing space.

Numbers represented in the explicit point scaled notation shall be output in the format significand E sign integer where the value x of the significand is in the range 1 <= x < 10 and is to be represented with exactly d digits of precision, and where the exrad component has one to e digits. Trailing zeroes may be omitted in the fractional part of the significand and leading zeroes may be omitted from the exrad. This form requires up to d+e+5 characters counting the two signs, the full- stop, the "E" and a trailing space.

String-expressions shall be evaluated to generate a string of characters.

The evaluation of the semicolon separator shall generate the null string, i.e. a string of zero length.

The evaluation of a tab-call or a comma separator depends upon the string of characters already generated by the current or previous print-statements. The "current line" is the (possibly empty) string of characters generated since the last end-of- line was generated. The "margin" is the number of characters, excluding the end-of-line character, that can be output on one line and is defined by the implementation. The "columnar position" of the current line is the print position that will be occupied by the next character output to that line; print positions are numbered consecutively from the left, starting with position one.

Each print-line is divided into a fixed number of print zones, where the number of zones and the length of each zone is implementation defined. All print zones, except possibly the last one on a line, shall have the same length. This length shall be at least d+e+6 characters in order to accomodate the printing of numbers in explicit point scaled notation as described above and to allow the comma separator to move the printing mechanism to the next zone as described below.

The purpose of the tab-call is to set the columnar position of the current line to the specified value prior to printing the next print-item. More precisely, the argument of the tab-call is evaluated and rounded to the nearest integer n. If n is less than one, an exception occurs. If n is greater than the margin m, then n is reduced by an integral multiple of m so n - m * INT ((n-l)/m).

If the columnar position of the current line is less than or equal to n, then spaces are generated, if necessary, to set the columnar position to n;

if the columnar position of the current line is greater than n, then an end-of-line is generated followed by enough spaces to set the columnar position of the new current line to n. The evaluation of the comma-separator generates one or more spaces to set the columnar position to the beginning of the next print zone, unless the current print zone is the last on the line, in which case an end-of-line is generated.

If the print list does not end in a print-separator, then an end-of-line is generated and added to the characters generated by the evaluation of the print-list.

If the evaluation of any print-item in a print-list would cause the length of a nonempty line to exceed the margin, then an end-of-line is generated prior to the characters generated by that print-item. Subsequently, if the evaluation of a print- item generates a string whose length is greater than the margin, then end-of-lines are inserted after every m characters in the string, where m is the margin value.

14.5 Exceptions

The evaluation of a tab-call argument generates a value less than one (nonfatal: the recommended recovery procedure is to supply one and continue).

14.6 Remarks

The comma-separator allows the programmer to tabulate the printing mechanism to fixed tab settings at the end of each print zone . A completely empty print-list will generate an end-of-line, thereby completing the current line of output. If this line contained no characters, then a blank line results. A print line on a typical terminal might be divided into five print zones of fifteen print positions each.

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