Excel Add-in Development in C/C++: Applications in ... - F9

12 Excel Add-in Development in C/C++Table 2.3 (continued)Literal arrays are enclosed in curly braces { and }, row-by-row (sometimesreferred to as row-major). Row elements are delimited by commas, androws themselves are delimited by semi-colons. For example, {1, “A”;TRUE, NA()} represents the 2 × 2matrix[1 ATRUE #N/A]2.5 EXCEL INPUT PARSERWhen a user types input to a cell in Excel and commits the data (by pressing enter, tabor selecting another cell), Excel performs several operations in the order outlined below.In essence, it is attempting to guess what kind of input the user was providing, and thentries to interpret accordingly. Understanding the order in which Excel does these thingsmay help you when creating your own functions or commands.1. If the input starts with a string prefix (a single quote mark) Excel places all of theinput characters in the cell as typed, with no modification. (The string prefix is notdisplayed.) If the input begins with =, + or -, it assumes a formula and uses its formulaparser to check the syntax. An error dialog appears if the formula does not make sense.Otherwise Excel will try and figure out if the user typed something that looked like adate, a time, a currency amount, a percentage, or just a number. If none of these, itreverts to considering the input as a string and places it in the cell unchanged.Note: This tendency to recognise dates and times before text can be quite annoying,especially if you intended to input a string such as the ratio “2:1”. Excel willchange the format of the cell to a time format and convert the input to the numericvalue 0.084027777 (the fraction of the day that has passed at 02:10 a.m.). Having toremember to prefix such inputs with a single quote mark can be frustrating.2. Where the input is seen as a possible formula, Excel attempts to identify, convert andevaluate function arguments and nested functions starting with the innermost, i.e., mostnested. Cell references and ranges are converted to values, which are then convertedto the right data types if necessary and so on. Where a token that is not recognised asa function or defined name is encountered, the conversion and evaluation fails with a#NAME? error. Otherwise defined names are converted just as the cells or expressionsthey represent would be.3. Once the input has been accepted, Excel attempts to recalculate those things thatdepend on the new input. If the input was a number and cell previously contained anumber, Excel will only recalculate if the value has changed. If a new formula has beenentered with references to new inputs, Excel verifies that no circular references havebeen created by this new formula. If a cell does depend on inputs which themselvesdepend on the value of this cell, Excel complains.4. Depending on the optional Excel or cell format settings, Excel may resize the columnwidth or row height.2.6 DATA TYPE CONVERSIONExcel always attempts to convert data from one type to another where required. Thissection explains when Excel tries to do this, and when it is and is not successful.