Dicom expression may be dimensional or dimension-less. You can intuitively write an expression, not so complicated, without knowing any rule.
For example: "1+2*3/4" is a simple dimension-less expression, and "3ft.+1m." is a simple dimensional expression.
Precedence and Associativity rule in Dicom is similar to C/C++ or any other programming language statement. In fact Dicom's operators are a subset of C++ language operators. Some of the functions of Dicom also behave like C/C++ functions.
Apart from the common operators like +, -, *, /, etc. Dicom deals with numerous other operators. Those are listed in Operator Reference in order of their precedence. You can also find this list in Dicom Explorer.
| General Rules | |
| 1 |
You can write expressions in a Dicom Document or Dicom Calculator. Usually a Document is used to calculate many related expressions for a particular task. For ad-hoc calculation Calculator can be used. |
| 2 |
Enclose any expression within the begin and end tags when you are writing in a Document. The default begin tag and end tag are [' and '] respectively. So, to evaluate 1+2*3/4 in a document, you have to write ['1+2*3/4']. |
| 3 |
You can define suitable begin and end tag of your choice, by using _DOC:, _BEGIN, and _END commands. |
| 4 |
Do not use any tag when you are writing expression in Calculator. |
| 5 |
Use ";" (semicolon) to separate expressions or commands. Example: length in {inch.}; area in {inch.}^2; x=5 ft; mArea=x^2 |
| Rules for Dimension | |
| 6 |
Allowable operators in a dimension are as follows: * : Multiplication operator. Associativity is left to right. No operator between two units also mean multiplication. / : Division operator. Associatively is left to right. ^ or ** : Exponentiation operator. Exponentiation has higher precedence than multiplication or division. |
| 7 |
Dot, [], or {} with a unit are optional, Example: {acre.} is same as acre |
| 8 |
Blank between two units is optional if dot is used. Example: acre.ft. Blank between two units is necessary if dot, [] or {} is not used. Example: acre ft |
| 9 |
A * can also be used to mean multiplication. Example: acre*ft |
| 10 |
Use / in case of per. Example: Btu./h./sft. This is not same as Btu./h.sft. The second unit means Btu./(h.sft.) |
| 11 |
If you do not know the exact symbol for writing a particular unit, you can select it from the explorer. |
| 12 |
To convert one unit to another in an expression, you can use converter operator ("to" or "->"). For example, to convert ft. to {inch.} write ft.-> {inch.} or ft. to {inch.} the result will be obviously 12 {inch.} |