1.7. Basic Compiler

Version I.5, September 1978

This section is designed for programmers who are already familiar with Basic. Its intent is to describe to those experienced users the details of UCSD Basic in a manner sufficiently detailed so as to enable the writing or modification of programs to be compatible with the UCSD Basic Compiler.

The first section contains a brief description of the features included in UCSD Basic; the second, the descriptions of the features unique to UCSD Basic, and the third a list of those features which we intend UCSD Basic to allow, but which are not yet implemented.

The UCSD Basic Compiler has been written in the Pascal language. Some of the intrinsics of the Pascal language, which are not found in standard Basic, are found within the UCSD version of Basic. Many of these are noted in the first section, all of them are noted or recapped in the second.

|IX SYSTEM.COMPILER

Description of Features Included

Variable Names

String variables: letter(digit)$. The digit is optional.

Intrinsic Arithmetic Functions

ATN(x)

Returns the angle in radians whose tangent is x.

EXP(x)

Returns the base of the natural logarithm raised to the power x.

INT(x)

Returns the value of x rounded to the nearest integer.

LOG(x)

Returns the log (base 10) of x.

LN(x)

Returns the natural log of x.

MOD(x, y)

Returns x modulo y.

SIN(x)

Returns the sine of the angle x, where x is in radians.

COS(x)

Returns the cosine of an angle x, where x is in radians.

Intrinsic String Functions

CAT$(s1, s2, ...)

Returns a string which is equal to the concatenation of all the strings in the parameter list.

COP$(s1, x, y)

Returns a copy of the portion of the string s1, y consecutive characters, starting with the character at position x.

DEL$(s1, x, y)

Returns the contents of the string s1 with y consecutive characters deleted. The deletion starts with the character at position x.

INS$(s1, s2, x)

Returns the contents of string s2 with string s1 inserted immediately before the character which is at position x.

LEN(s1)

Returns the length of the string s1.

POS(s1, s2)

Returns an integer which is equal to the position of the first character in the first occurrence of the string s1 in the string s2.

Other Functions

ORD(s)

Returns the ASCII value of the first character of the string s.

STR$(x)

Returns the string containing the character associated with the ASCII value x.

GET$

Reads a single character from the keyboard without prompt or echoing, and returns it as a string. GET$ requires no arguments.

OLD(c, s)

NEW(c, s)

c is a numeric constant without a fraction part, which becomes associated with the disk file whose name is in s. OLD expects that file to already exist, NEW creates a new one with the name s, removing any previous file of that name. These functions must occur before associated print or input statements. The numbers may not be reassigned and must be in the range 1..16. For best results, use only at the top of a program. In order that a file created by NEW be editable with either of the system editors, ‘.TEXT’ must be appended to the file title.

These functions return IORESULT as described in section 2.1.

Arithmetic Operators

Relational operators

Programming Statements

INPUT list

INPUT #c list

Inputs from the main system device, usually the keyboard. If the optional #c is present, INPUT inputs from the disk file number c. The input list may contain any combination of real variables and string variables. When a program expects input the prompt “?” is printed. Input of real numbers may be terminated with any non-numeric character. Input of strings must be terminated with a return.

PRINT list

PRINT #c list

Writes to the main output device the list following the PRINT command. If the optional #c is present, PRINT outputs to the diskfile number c. The output list may contain any variable, subscripted array variable, any arithmetic or string expression, or any literal text. The list may be separated by commas or semi-colons. If the list ends in a semi-colon the carriage return is suppressed. Literals may be enclosed in either type of quotation marks. Double quotation marks prints a single quotation mark.

FOR var = exp1 TO exp2 STEP exp3

NEXT var

Each execution of the loop increments the loop counter “var” by the amount of the third expression. If the STEP is omitted it is assumed to be 1. Only increasing STEP values are allowed. Evaluation of limits and increments is done at the beginning of the loop. Note that RETURNs into or GOTOs into a FOR loop may cause the loop to be undefined.

IF exp1 (relation operator) exp2 THEN (line number)

IF exp1 (relation operator) exp2 GOTO (line number)

Either the reserved word THEN or GOTO can be used in this statement. If the relation between the exp1 and exp2 is found to be true the branch occurs. A string is considered to be less than another string if it is lexicographically smaller.

ON exp GOTO (ln1, 1n2 ...)

If the expression, when rounded, evaluates to 1 it goes to the first line number (ln1), if it evaluates to 2 it goes to ln2, etc. This is the only form of the computed GOTO which is available. If the expression is out of range an error occurs.

DEF FNname(list) = expression

DEF FNname(list)
:
FNEND

Single line and multi-line functions are allowable. The function name must be a legal variable name for the type of value returned. Functions may be defined recursively. The parameter list is called by value, that is, changes inside the function don't affect the value of the external parameters.

LET var = exp

var = exp

This command assigns a new value to the variable. If the variable is a string, the expression must evaluate to a string. If the variable is a real, the expression must evaluate to a real.

DIM var (n1, n2, ...)

A single or multi-dimensional array may be declared with this command. The variable name determines the type of the array. The array indices are 0..n1, 0..n2, ... Both real and string multidimensional arrays can be used. If no dimensions are declared the dimensions are assumed to be 0..1O, 0..1O, 0..1, 0..1, ... The number of dimensions automatically declared depends on the number of dimensions which are used in the program, but must be consistent over all uses of any given array.

GOSUB line-number

Executes a subroutine call. The calling address is placed on the subroutine stack. Subroutine calls may be recursive.

RETURN

Returns to the line after the last GOSUB which is still pending. It pops the top address off the stack and uses it as the return address. A return when no GOSUBs are pending is an error.

GOTO line-number

Program execution jumps to the given line number.

REM text This line is a remark (a comment).

Unique Features of UCSD Basic

For loops:

Note that var = exp1 is done before exp2 or exp3 are evaluated.

Continuation of statements is allowed.

Any line not beginning with a line number is assumed to be the continuation of the line above.

Functions:

All parameters of functions are call by value. You are not allowed to use the parameters to return values from a function. Function calls are allowed to be recursive.

Strings:

The string functions and procedures are those found in the UCSD Pascal language.

Arrays:

Arrays of more than two dimensions are allowed.

Print:

Tab stops are not allowed. All list elements are printed without spaces between them. The carriage return can be suppressed by “;” as the last symbol in the line.

Subroutines:

Subroutines may be recursive.

Comments:

In line comments may be inserted. The portion of any line following the “@” symbol is ignored by the compiler.

PASCAL FUNCTIONs:

The code of PASCAL FUNCTIONs may be added to the BASIC compiler as new standard BASIC functions. This is accomplished by a straight-forward addition to the BASIC compiler.

Features to be Added

Data and Read:

The standard initialization statements.

Matrix

A MATRIX statement for standard matrix operations.

Integer variables.

and expressions.

Functions

More standard functions.

Running a Basic Program