"The function fgets (short for file get string) using the keyword STDIN (Standard Input) returns, as a string, everything the user enters up to and including the enter key, interpreted as the endline character. To remove the endline character, you can use trim, which removes leading and trailing whitespace from a string. A full example is: printf(\"Please enter a number: \"); $a = fgets(STDIN); $a = trim($a); Alternatively, lines 3–4 could be combined into one: $a = trim(fgets(STDIN)); The call to fgets waits, referred to as “blocking,” for the user to enter input. The user is free to start typing, and when they are done, they hit the enter key, at which point the program resumes, reads the input from the standard input buffer, and returns it as a string value assigned to the variable $a. Standard input is unstructured, so the user is free to type whatever they want. If we prompt the user for a number but they enter non-numerical input, we may get incorrect results. We can use conversion functions to attempt to properly convert the values, although this only guarantees that the resulting variable is of the type we want, such as an integer or floating-point value. Standard input is not a good mechanism for reading input, but it provides a good starting point for developing a few simple programs."