![]() | Chapter 15: Tables | ![]() ![]() |
15.7. Blank entries |
We are allowed to leave certain entries blank (perhaps to be filled in later, perhaps not) by writing "--" instead of the relevant value:
Table 2.1 - Selected Elements
Element Symbol Atomic number Atomic weight "Hydrogen" "H" 1 1 "Iron" "Fe" -- 56 "Zinc" -- 30 65 "Uranium" "U" 92 238
In effect, blank entries don't exist. "--" is not a value, but only a hole where a value might be. It can be useful to check for this:
if there is (a table entry):
This condition is true if the entry referred to exists, that is, that is, the space for it in the table is not blank. Examples:
if there is a symbol corresponding to an atomic number of 30 in the Table of Standard Elements ...
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if there is no (a table entry):
This condition is true if the entry referred to does not exist, that is, the space for it in the table is blank. Examples:
if there is no symbol corresponding to an atomic number of 30 in the Table of Standard Elements ...
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