The value of an awk expression is always either a number
or a string.
Some contexts (such as arithmetic operators) require numeric values. They convert strings to numbers by interpreting the text of the string as a number. If the string does not look like a number, it converts to zero.
Other contexts (such as concatenation) require string values.
They convert numbers to strings by effectively printing them
with sprintf.
See section Conversion of Strings and Numbers, for the details.
To force conversion of a string value to a number, simply add zero to it. If the value you start with is already a number, this does not change it.
To force conversion of a numeric value to a string, concatenate it with the null string.
Comparisons are done numerically if both operands are numeric, or if
one is numeric and the other is a numeric string. Otherwise one or
both operands are converted to strings and a string comparison is
performed. Fields, getline input, FILENAME, ARGV
elements, ENVIRON elements and the elements of an array created
by split are the only items that can be numeric strings. String
constants, such as "3.1415927" are not numeric strings, they are
string constants. The full rules for comparisons are described in
section Variable Typing and Comparison Expressions.
Uninitialized variables have the string value "" (the null, or
empty, string). In contexts where a number is required, this is
equivalent to zero.
See section Variables, for more information on variable naming and initialization; see section Conversion of Strings and Numbers, for more information on how variable values are interpreted.
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