BASIC-DOS

BASIC-DOS Screen Commands

Screen commands include:

• CLS
• COLOR
• ECHO
• LOCATE
• PRINT
• SCREEN
• WIDTH

Each session has its own console, which may occupy only part of the screen (see Sessions). Screen commands operate on the current session’s console, and coordinates are relative to the console, not the screen.

When a BAS program that used a graphics mode ends (or is aborted), the video mode it started with is restored, along with the console’s original size and border, even if the program returned to a text mode first (eg, DONKEY.BAS, whose SCREEN 0 leaves 40 columns); otherwise, text-mode changes (eg, WIDTH 40 or SCREEN 0,0) persist, as in Microsoft BASIC.

CLS

CLS

Clears the console using the background color and moves the cursor to the top left corner.

COLOR

COLOR [foreground][,[background][,border]]

Sets the foreground (0-15), background (0-7), and border (0-255) colors of the console. For blinking colors, use 16-31 for foreground and 128-255 for border; as in MSBASIC, a background of 8-15 is the same as 0-7 (it doesn’t make the foreground blink). Omitted values are unchanged (eg, COLOR ,1).

In SCREEN 1, the values are the background color (0-15) and palette (0 or 1) instead.

The colors are:

ECHO

ECHO [ON

OFF]

Controls the echo of lines in a BAT file. After ECHO ON, a BAT file echoes each line before running it, until ECHO OFF is used; a line beginning with @ is never echoed (eg, @ECHO ON). Echoed lines are displayed with a @ in front (eg, @REM Starting), where PC DOS would display a prompt. ECHO without ON or OFF displays the current setting.

Every BAT file run from the prompt (or by a startup command) starts with ECHO OFF, unlike PC DOS, so BAT files behave like BAS files unless ECHO ON is used; the setting remains in effect when one BAT file runs another. BAS files never echo their lines. A @ at the start of a command typed at the prompt is ignored, as in later versions of PC DOS.

LOCATE

LOCATE [row][,[col][,cursor]]

Moves the cursor to the specified row and col (starting at 1,1), and hides (0) or shows (1) the cursor. The cursor remains hidden until the next input. Omitted values are unchanged.

PRINT

PRINT [expression][;

,][expression]…

Prints a series of values, separated by semicolons or commas. A semicolon prints the next value immediately after the previous one, and a comma prints a tab. Numbers are printed with a leading space (or minus sign) and a trailing space. If the list ends with a semicolon or comma, the cursor remains on the same line; otherwise, PRINT moves to the next line. PRINT # writes the same output to a file.

PRINT "A"; 1; "B", 2
A 1 B	 2

On the PC’s display, as in PC DOS, control characters other than BELL (7, which beeps), BACKSPACE (8), TAB (9), LINEFEED (10), and RETURN (13) are displayed as the PC’s graphic characters (eg, PRINT CHR$(14) displays a musical note); unlike IBM PC BASIC, characters such as CHR$(12) and CHR$(28)-CHR$(31) don’t clear the screen or move the cursor. On a serial console, they’re sent to the terminal as they are.

PRINTF

PRINTF USING format;[value][,

;][value]…

Prints the values using the C-style specifiers in format, as a simpler alternative to the PRINT USING of other BASICs. Each % specifier takes the next value: %d or %u prints a number (%x in hexadecimal, and %#d with a leading space for positive numbers, like PRINT), %f prints a double (BASIC-style unless a precision is given), %s prints a string, and %c prints a character (from a number or the first character of a string). Specifiers accept the - flag (left-justify), a width, and a precision (eg, %5d, %-8.3s, %.2f), and %% prints a percent sign. Other specifiers print part of a number that holds a packed DOS date or time (eg, from a DIR$ entry): %M, %D, and %Y print a date’s month, day, and year (%X prints the year with 2 digits), %F and %W print the names of its month and day of the week (eg, %.3F prints Oct), and %H, %N, and %S print a time’s hour, minute, and second (%G prints a 12-hour hour, and %A prints a or p). Since the values carry their own types, size modifiers like l are unnecessary, and a value of the wrong type prints its specifier unchanged. As with PRINT, the cursor moves to the next line unless the list ends with a semicolon or comma. PRINTF # writes the same output to a file.

PRINTF USING "%-6s|%5d|%.2f"; "abc", 42, 3.14159
abc   |   42|3.14

Comma print zones aren’t supported yet (commas currently print a tab). PRINT USING isn’t supported, and won’t be, since PRINTF USING covers the same needs (see below).

How to replace PRINT USING

The PRINT USING (and LPRINT USING) statement of other BASICs formats values with templates, such as "###.##". To convert one to PRINTF USING, replace each field of the template with the corresponding specifier:

The other differences to watch for:

• Repeating fields: PRINT USING reuses its template for each value, but PRINTF USING uses each specifier once (and ignores extra values), so repeat the specifiers instead (eg, PRINT USING "###";A;B;C becomes PRINTF USING "%3d%3d%3d";A;B;C).
• Types: %d requires an integer and %f requires a double, and a value of the wrong type prints its specifier as-is. Variables without a suffix are doubles in BAS files but integers in BAT files, and constants without a decimal point or exponent (eg, 42) are integers (see Variables and Types), so use CINT or CDBL to convert a value when necessary (eg, PRINTF USING "%3d";CINT(I)).
• Overflow: when a number doesn’t fit in its field, PRINT USING prints a % before it, but PRINTF simply widens the field.
• Rounding: PRINTF rounds a number that’s exactly halfway to the nearest even digit (eg, %.0f prints 2.5 as 2), whereas PRINT USING rounds it up.

For example, the MORTGAGE.BAS sample (in the SAMPLES directory) printed its amortization table with:

2730 PRINT USING "### ";I;
2740 PRINT USING "  ######.##";PF-AMORT(I,2);AMORT(I,2);AMORT(I,1)

and now prints it with:

2730 PRINTF USING "%3.0f ";I;
2740 PRINTF USING "  %9.2f  %9.2f  %9.2f";PF-AMORT(I,2);AMORT(I,2);AMORT(I,1)

LPRINT

LPRINT [expression][;

,][expression]…

Prints like PRINT, but to the printer (PRN, which is the first parallel port, LPT1). If there’s no printer (eg, the machine has no parallel port), a “Device timeout” error occurs after the statement, and a printer can also report “Out of paper” or “Device fault”; PRINT # to a printer (eg, a file opened as “PRN” or “LPT2”) reports the same errors. See also LLIST and LPOS. LPRINT USING isn’t supported; to format output for the printer, open PRN as a file and use PRINTF #n (see How to replace PRINT USING). LPRINT isn’t available on low memory systems.

LPRINT "Total:"; T

SCREEN

SCREEN [mode][,burst]

Sets the screen mode on a color adapter:

• 0: text
• 1: 320x200 graphics (4 colors)
• 2: 640x200 graphics (2 colors)

A burst of 0 disables color in mode 0, and a burst of 1 disables color in mode 1. Changing the mode clears the screen and removes the console’s border, if any, so the console occupies the entire screen. Text output (eg, PRINT) works in all modes.

While a session is in any mode other than its original mode (eg, a graphics mode, or 40 columns in an 80-column session), it uses the entire screen, so other sessions on the same display are paused: any output they produce waits until that session returns to its original mode (eg, when its BAS program ends, which restores the mode), and then their borders are redrawn and their output continues. Their earlier screen contents are not restored.

WIDTH

WIDTH 40|80
WIDTH device,width

Sets the number of columns in text mode (which clears the screen). In SCREEN 1, WIDTH 80 selects SCREEN 2, and in SCREEN 2, WIDTH 40 selects SCREEN 1.

With a device name (a string), WIDTH "SCRN:",width is the same as WIDTH width. For any other device (eg, WIDTH "COM1:",255), Microsoft BASIC sets the line width of the device’s output (where 255 means lines are never broken), but BASIC-DOS never breaks a device’s output into lines, so the width (1-255) is only checked, for compatibility. WIDTH device isn’t available on low memory systems (see Low Memory).

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