Information at all times was a symbol. Only when programming appeared did it partially become letters, numbers and signs (in the formal sense).
Until a certain time, oral speech, hand-made characters, gestures, as well as works of art, in particular, enjoyed the greatest popularity. It is important that all these options for the natural presentation of information, from small to large, could always be described in words, that is, made available to software processing in one sense or another.
Lines and numbers
Strings are, first of all, collections of different characters. In different programming tools, the fractional part was separated from the whole in different ways. Some preferred a period, others a comma (in PHP, converting a string to a number implies a "."). The triads were separated by a single apostrophe, comma or space. Real numbers were written through the letter "E".
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Converting in PHP " string to number" rather indicates that we can, but mathematics and numerical calculations are not our thing.
Writing a decent and reliable functional that implements this or that number processing in PHP is not a problem, and the result will not be any worse than the result from more mathematical languages. PHP is, first of all, the server language, a language for processing information, including mathematical ones.