A function giving the absolute value of its argument.

This function converts negative numbers into positive ones. It can be used to give the difference between two numbers without regard to the sign of the answer.

It is particularly useful when you want to know the difference between two values, but you don’t know which is the larger. For instance, if X=6 and Y=10 then the following examples would give the same result.

You can use this function to check that a calculated answer is within certain limits of a specified value. For example, suppose you wanted to check that 'answer' was equal to 'ideal' plus or minus (up to) 0.5. One way would be:

However, the following example would be a more elegant solution.

A function giving the arc cosine of its argument in radians. The permitted range of the argument is -1 to +1.

If you know the cosine of the angle, this function will tell you the angle (in radians). Unfortunately, you cannot do this with complete certainty because two angles within the range /- PI (/- 180 degrees) can have the same cosine. This means that one cosine has two associated angles.

The following diagram illustrates the problem:

Within the four quadrants, there are two angles which have the same cosine, two with the same sine and two with the same tangent. When you are working back from the cosine, sine or tangent you don’t know which of the two possible angles is correct.

By convention, ACS gives a result in the top two quadrants (0 to PI - 0 to 180 degrees) and ASN and ATN in the right-hand two quadrants (-PI/2 to +PI/2 - -90 to + 90 degrees).

In the example below, 'radian_angle' becomes equal to the angle (in radians) whose cosine is 'y'.

You can convert the answer to degrees by using the DEG function (or multiplying by 180/PI).

This function returns information about the analogue to digital converter channels on the Games Adapter card (if fitted). The information returned depends upon the argument passed to ADVAL.

Not implemented

The operation of integer bitwise logical AND between two items. The 2 operands are internally converted to four byte integers before the AND operation.

You can use AND as a logical operator or as a 'bit-by-bit' (bitwise) operator. The operands can be boolean (logical) or numeric.

In the following example program segment, AND is used as a bitwise operator to remove the most significant bit of a byte read from a file before writing it to another file. This is useful for converting some word-processor files into standard ASCII format.

Unfortunately, BBC BASIC does not have true boolean variables; it uses numeric variables and assigns the value 0 for FALSE and -1 for TRUE. This can lead to confusion at times. (See NOT for more details.) In the example below, the operands are boolean (logical). In other words, the result of the tests (IF) A=2 and (IF) B=3 is either TRUE or FALSE. The result of this example will be TRUE if A=2 and B=3.

The brackets are not necessary, they have been included to make the example easier to follow.

The second example is similar to the first, but in the more familiar surroundings of an IF statement.

or

The final example, uses the AND in a similar fashion to the numeric operators (+, -, etc).

Suppose X was -20, the AND operation would be:

A function returning the ASCII character value of the first character of the argument string. If the string is null then -1 will be returned.

A computer only understands numbers. In order to deal with characters, each character is assigned a code number. For example (in the ASCII code table) the character 'A' is given the code number 65 (decimal). A part of the computer generates special electronic signals which cause the characters to be displayed on the screen. The signals generated vary according to the code number.

You could use this function to convert ASCII codes to some other coding scheme.

|== |ascii_code=ASC("H") |Result would be 72 |X=ASC("HELLO") |Result would be 72 | | |name$="FRED" | |ascii_code=ASC(name$) |Result would be 70 |X=ASC"e" |Result would be 101 | | |X=ASC(MID$(A$,position)) |Result depends on A$ and position. |==

ASC is the complement of CHR$.

A function giving the arc sine of its argument in radians. The permitted range of the argument is -1 to +1.

By convention, the result will be in the range -PI/2 to +PI/2 (-90 to +90 degrees).

If you know the sine of the angle, this function will tell you the angle (in radians). Unfortunately, you cannot do this with complete certainty because one sine has two associated angles. (See ACS for details.)

In the example below, 'radian_angle' becomes equal to the angle (in radians) whose sine is 'y'.

You can convert the answer to degrees by using the DEG function. (The DEG function is equivalent to multiplying by 180/PI.) The example below is similar to the first one, but the angle is in degrees.

A function giving the arc tangent of its argument in radians. The permitted range of the argument is from - to + infinity.

By convention, the result will be in the range -PI/2 to +PI/2 (-90 to +90 degrees).

If you know the tangent of the angle, this function will tell you the angle (in radians).

As the magnitude of the argument (tangent) becomes very large (approaches + or - infinity) the accuracy diminishes.

In the example below, 'radian_angle' becomes equal to the angle (in radians) whose tangent is 'y'.

You can convert the answer to degrees by using the DEG function. (The DEG function is equivalent to multiplying by 180/PI.) The example below is similar to the first one, but the angle is in degrees.

A command allowing the user to enter lines without first typing in the number of the line. The line numbers are preceded by the usual prompt (>).

You can use this command to tell the computer to type the line numbers automatically for you when you are entering a program (or part of a program).

If AUTO is used on its own, the line numbers will start at 10 and go up by 10 for each line. However, you can specify the start number and the value by which the line numbers will increment. The step size can be in the range 1 to 255.

You cannot use the AUTO command within a program or a multi-statement command line.

You can leave the AUTO mode by pressing the escape key.

|== |AUTO |offers line numbers 10, 20, 30 …​ |AUTO 100 |starts at 100 with step 10 |AUTO 100,1 |starts at 100 with step 1 |AUTO ,2 |starts at 10 with step 2 |==

A hyphen is an acceptable alternative to a comma.

A function which gets a byte from the file whose file handle is its argument. The file pointer is incremented after the byte has been read.

You must normally have opened a file using OPENOUT, OPENIN or OPENUP before you use this statement. (See these keywords and the BBC BASIC (Z80) Disk Files section for details.) BGET# may alternatively be used with the AUX device (usually a serial port) which has the 'permanently open' handle = 3.

You can use BGET# to read single bytes from a disk file. This enables you to read back small integers which have been 'packed' into fewer than 5 bytes (see BPUT#). It is also very useful if you need to perform some conversion operation on a file. Each byte read is numeric, but you can use CHR$(BGET#n) to convert it to a string.

The input file in the example below is a text file produced by a word-processor.

Words to be underlined are 'bracketed' with ^S. The program produces an output file suitable for a printer which expects such words to be bracketed by ^Y. You could, of course, perform several such translations in one program.

To make the program more useful, it could ask for the names of the input and output files at 'run time':

A statement which puts a byte to the data file whose file handle is the first argument. The second argument’s least significant byte is written to the file. The file pointer is incremented after the byte has been written.

Before you use this statement you must normally have opened a file for output using OPENOUT or OPENUP. (See these keywords and the BBC BASIC (Z80) Disk Files section for details.) BPUT# may alternatively be used with the AUX device (usually a serial port), which has the 'permanently open' handle = 3, or the PRN device (usually a parallel port) which has the 'permanently open' handle = 4.

You can use this statement to write single bytes to a disk file. The number that is sent to the file is in the range 0 to 255. Real numbers are converted internally to integers and the top three bytes are 'masked off'. Each byte written is numeric, but you can use ASC(character$) to convert (the first character of) 'character$' to a number.

The example below is a program segment that 'packs' an integer number between 0 and 65535 (&FFFF) into two bytes, least significant byte first. The file must have already been opened for output and the file handle stored in 'fnum'. The integer variable number% contains the value to be written to the file.

A statement to call a machine code subroutine.

The processor’s A, B, C, D, E, F, H and L registers are initialised to the least significant words of A%, B%, C%, D%, E%, F%, H% and L% respectively (see also USR).

A statement which loads and runs the program whose name is specified in the argument.

The program file must be in tokenised format.

All but the static variables @% to Z% are CLEARed.

CHAIN sets ON ERROR OFF before chaining the specified program.

RUN may be used as an alternative to CHAIN.

You can use CHAIN (or RUN) to link program modules together. This allows you to write modular programs which would, if written in one piece, be too large for the memory available.

Passing data between CHAINed programs can be a bit of a problem because COMMON variables cannot be declared and all but the static variables are cleared by CHAIN.

If you wish to pass large amounts of data between CHAINed programs, you should use a data file. However, if the amount of data to be passed is small and you do not wish to suffer the time penalty of using a data file, you can pass data to the CHAINed program by using the indirection operators to store them at known addresses. The safest way to do this is to move HIMEM down and store common data at the top of memory.

The following sample program segment moves HIMEM down 100 bytes and stores the input and output file names in the memory above HIMEM. There is, of course, still plenty of room for other data in this area.

A function which returns a string of length 1 containing the ASCII character specified by the least significant byte of the numeric argument.

CHR$ generates an ASCII character (symbol, letter, number character, control character, etc) from the number given. The number specifies the position of the generated character in the ASCII table (See Annex A). For example:

will set char$ equal to the character 'A'. You can use CHR$ to send a special character to the terminal or printer. (Generally, VDU is better for sending characters to the screen.) For example,

will generate the ASCII character ^G. So,

will print the message 'ERROR' and sound the PC’s 'bell'.

CHR$ is the complement of ASC.

A statement which clears all the dynamically declared variables, including strings. CLEAR does not affect the static variables.

The CLEAR command tells BBC BASIC (Z80) to 'forget' about ALL the dynamic variables used so far. This includes strings and arrays, but the static variables (@% to Z%) are not altered.

You can use the indirection operators to store integers and strings at known addresses and these will not be affected by CLEAR. However, you will need to 'protect' the area of memory used. The easiest way to do this is to move HIMEM down. See CHAIN for an example.

A statement used to close a data file. CLOSE #0 will close all data files.

You use CLOSE# to tell BBC BASIC (Z80) that you have completely finished with a data file for this phase of the program. Any data still in the file buffer is written to the file before the file is closed.

You can open and close a file several times within one program, but it is generally considered 'better form' not to close a file until you have finally finished with it. However, if you wish to CLEAR the variables, it is simpler if you close the data files first.

You should also close data files before chaining another program. CHAIN does not automatically close data files, but it does clear the variables in which the file handles were stored. You can still access the open file if you have used one of the static variables (A% to Z%) to store the file handle. Alternatively, you could reserve an area of memory (by moving HIMEM down for example) and use the byte indirection operator to store the file handle. (See the keyword CHAIN for more details.)

END or 'dropping off' the end of a program will also close all open data files. However, STOP does not close data files.

A statement which clears the graphics area of the screen and sets it to the currently selected graphics background colour,

A statement which clears the text area of the screen and sets it to the currently selected text background colour. The text cursor is moved to the 'home' position (0,0) at the top left-hand corner of the text area.

Change the the current text output colour.

Note, since BBC BASIC is British, the British spelling of "colour" is the default. The US spelling is however recognised as an alternative.

The following two commands are only applicable to paletted modes with fewer than 64 colours.

Set the logical colour l to the physical colour p

Set the logical colour l to the physical colour represented by the RGB value where r(ed), g(reen) and b(lue) are each specified as a base 10 integer value in the range 0-255.

A function giving the cosine of its radian argument.

This function returns the cosine of an angle. The angle must be expressed in radians, not degrees.

Whilst the computer is quite happy dealing with angles expressed in radians, you may prefer to express angles in degrees. You can use the RAD function to convert an angle from degrees to radians.

The example below sets Y to the cosine of the angle 'degree_angle' expressed in degrees.

A function returning the number of characters sent to the output stream (VDU or printer) since the last new line.

Characters with an ASCII value of less than 13 (carriage return/new-line/enter) have no effect on COUNT.

Because control characters above 13 are included in COUNT, you cannot reliably use it to find the position of the cursor on the screen. If you need to know the cursor’s horizontal position use the POS function.

Count is NOT set to zero if the output stream is changed using the *OPT command.

The example below prints strings from the string array 'words$'. The strings are printed on the same line until the line length exceeds 65. When the line length is in excess of 65, a new-line is printed.

A program object which must precede declaration of a user defined function (FN) or procedure (PROC). DEF must be used at the start of a program line.

If DEF is encountered during execution, the rest of the line is ignored. As a consequence, single line definitions can be put anywhere in the program.

Multi-line definitions must not be executed. The safest place to put multi-line definitions is at the end of the main program after the END statement.

There is no speed advantage to be gained by placing function or procedure definitions at the start of the program.

In order to make the text more readable (always a GOOD THING) the function or procedure name may start with an underline.

Function and procedure names may end with a '$'. This is not compulsory for functions which return strings.

A procedure definition is terminated by the statement ENDPROC.

A function definition is terminated by a statement which starts with an equals (=) sign. The function returns the value of the expression to the right of the equals sign.

For examples of function and procedure declarations, see FN and PROC. For a general explanation of functions and procedures, refer to the Procedures and Functions sub-section in the General Information section.

A function which converts radians to degrees.

You can use this function to convert an angle expressed in radians to degrees. One radian is approximately 57 degrees (actually 180/PI). PI/2 radians is 90 degrees and PI radians is 180 degrees.

Using DEG is equivalent to multiplying the radian value by 180/PI, but the result is calculated internally to a greater accuracy.

See ACS, ASN and ATN for further examples of the use of DEG.

A command which deletes a group of lines from the program. Both start and end lines of the group will be deleted.

You can use DELETE to remove a number of lines from your program. To delete a single line, just type the line number followed by <Enter>.

The example below deletes all the lines between line 10 and 15 (inclusive).

To delete up to a line from the beginning of the program, use 0 as the first line number. The following example deletes all the lines up to (and including) line 120.

To delete from a given line to the end of the program, use 65535 as the last line number. To delete from line 2310 to the end of the program, type:

A hyphen is an acceptable alternative to a comma.

There are two quite different uses for the DIM statement: the first dimensions an array and the second reserves an area of memory for special applications.

A binary operation giving the integer quotient of two items. The result is always an integer.

You can use this function to give the 'whole number' part of the answer to a division. For example,

would give 5 (with a 'remainder' of 1).

Whilst it is possible to use DIV with real numbers, it is really intended for use with integers. If you do use real numbers, BBC BASIC (Z80) converts them to integers by truncation before DIViding them.

A statement which draws a line on the screen in the graphics modes. The statement is followed by the X and Y coordinates of the end of the line.

A command to edit specified lines. By changing only the line number, you can also use EDIT to duplicate a line.

To save your changes and exit the edit mode, press <Enter>.

To abort the single line editor and leave the line unchanged, press <Esc>.

A statement delimiter which provides an alternative course of action in IF…​THEN, ON…​GOSUB, ON…​GOTO and ON…​PROC statements.

In an IF statement, if the test is FALSE, the statements after ELSE will be executed. This makes the following work:

In a multi statement line containing more than one IF, the statement(s) after the ELSE delimiter will be actioned if ANY of the tests fail. For instance, the example below would print the error message ‘er$’ if 'x' did not equal 3 OR if 'a' did not equal 'b'.

If you want to 'nest' the tests, you should use a procedure call. The following example, would print 'Bad' ONLY if x was equal to 3 AND 'a' was not equal to 'b'.

You can use ELSE with ON…​GOSUB, ON…​GOTO and ON…​PROC statements to prevent an out of range control variable causing an 'ON range' error.

A statement causing the interpreter to return to direct mode. There can be any number (>=0) of END statements anywhere in a program. END closes all open data files.

END tells BBC BASIC (Z80) that it has reached the end of the program. You don’t have to use END, just 'running out of program' will have the same effect, but it’s a bit messy.

You can use END within, for instance, an IF…​THEN…​ELSE statement to stop your program if certain conditions are satisfied. You should also use END to stop BBC BASIC (Z80) 'running into' any procedure or function definitions at the end of your program.

A statement denoting the end of a procedure.

All local variables and the dummy arguments are restored at ENDPROC and the program returns to the statement after the calling statement.

A statement which is used, in conjunction with the SOUND statement, to control the pitch of a sound whilst it is playing.

Not implemented