A few simple questions about php

Questions for new php users. A few simple questions. 1. what is the difference between single quotes and double quotes in php. 2. php variable & nbsp; $ str = & quot; aa $ C & quot; & nbsp; and $ str = & quot; aa & quot ;. $ C is not just two different writing methods ., 1. strings in single quotes are not replaced with variables or escaped characters. Double quotation marks are a few simple questions for new php users.
1. what is the difference between single quotes and double quotes in php.
2. php variables $ str = "aa $ C" and $ str = "aa". $ C are just two different methods.



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1. Strings in single quotes are not replaced with variables or escaped characters. Double quotation marks replace variables and escape special characters.
2. yes
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Upstairs
Positive solution: Use points to make your program more readable.
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Same as above
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Test it with a program and you will understand everything.
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Variables in double quotation marks are parsed. No single quotation marks (output as is ).
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Learning
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Variables can be placed in double quotation marks, but not in single quotation marks. '$ str' will output $ str. because PHP considers that the single quotation mark is a string rather than a variable.
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Single quotes are highly efficient and support single quotes
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You put the variables in them separately, and then output them.