The text read off it
[page 45]
The second of these examples shows the way in which subexpressions may be contained in parentheses when required. Likewise, the examples taken together illustrate the use of each element which may appear in an arithmetic expression, viz., arithmetic operators, names of variables and constants, literals, truth functions, and function-names. Each of these elements is considered individually below even though it may be discussed in greater detail elsewhere in the manual. (The formal rules governing the formation of arithmetic expressions are given in Appendix 2.)
ARITHMETIC OPERATORS
The following arithmetic operators are used to join other elements to form meaningful arithmetic expressions:
| Operator | Written as |
|---|---|
| Addition | + |
| Subtraction | − |
| Multiplication | * |
| Division | / |
| Exponentiation | ** |
These operators are sometimes referred to as "binary" operators because each of them relates two quantities. There are three additional arithmetic operators known as "unary" operators. They are:
| Operator | Written as |
|---|---|
| Negation | − |
| Absolute value | ABS |
| Truth value | TR |
These operators affect only the quantity or expression which follows, hence the term unary. If the operand of a unary operator is an expression it must be enclosed in parentheses, as in these examples:
... + ABS (A + B)
... * (−(ON.HAND + ON.ORDER))
... TR (A IS LESS THAN B)
VARIABLES AND CONSTANTS
Data-names which represent numeric variables or constants may appear anywhere in arithmetic expressions. Those which represent alphameric variables and constants , however, may appear only within truth functions.
LITERALS
Literals may be used as needed in arithmetic expressions. Literals used in the above examples of the SET command are 40 in the first example and 2 in the fifth.
TRUTH FUNCTIONS
A conditional expression enclosed in parentheses preceded by the truth operator TR is known as a truth function. A truth function always has one of two values, 1 or 0, depending on whether the conditional expression is true or false.