Hello, the SA team defined a real variable for the given answer (the following answer is quoted from Baidu Encyclopedia): A real variable whose value can be changed during the running of the program is called a real variable. Real variables are divided into single precision (float), double precision (double) and long double precision (long double). In C language, real variables can be expressed in two forms. I. Fractional form II. Integer 1 in exponential form. Definition: Integer is the set z = {...,-2,-1,0,1,2, ...}. See: Integer /GMP with arbitrary length, floating-point number and mathematical library /BCMath with arbitrary precision. Discrete definition: the phenomenon that the contents in shear flow are longitudinally dispersed due to the uneven velocity distribution on the cross section. A character string or character string is a finite sequence of zero or more characters. The general record is s='a 1a2? 6? 1? 6? 1? 6? 1an '(n & gt； =0)。 It is a data type that represents text in programming language. Usually, the whole string is taken as the operation object, such as finding a substring in the string, finding a substring, inserting a substring at a certain position in the string, and deleting a substring. The necessary and sufficient conditions for two strings to be equal are: the length is equal, and the characters in each corresponding position are equal. Let p and q be two strings, and the operation of finding the position where q first appears in p is called pattern matching. The two most basic storage methods of strings are sequential storage and linked storage.