What is functional programming? Why is C language not a functional language?

• What is functional programming? Why is C language not a functional language?

  Functional languages ​​have two main characteristics: 1. Functions are "first class citizens". 2. The "immutability" of the data. The "no side effects" of the operation,
  which circumvents the " lock".
  The function of functional programming is an exponential function: given input, fixed output, no side effects. Any language can use a functional style,
  but the difficulty is different.
  For example, the function y = f(x). and the function t = g(z); In mathematics, when t is in the domain of f(x), it can form a composite function y=f(g(z));

• For the second question, why is C not a functional language?

  Because this effect cannot be achieved in C.

  int f(int x) { print x;} ===== y = f(x)
  int f1(int (*g)(int)) { print g(z);} ===== y = f1(g(z))
  int g(int z) {return z;}  =========  t = g(z)
  

  From the above function definition, we can see that when the parameter of the function f(x) is defined as int, the function g(z) cannot be passed to it as a formal parameter.
  On the other hand, the function f1() cannot accept int as a parameter.

  Therefore, C cannot achieve the kind of effect of mathematical functions.

  But in clojure it does.

  (defn f [x] (print x))    ======= y = f(x)
  (defn g [z] z)            ======= t = g(z)
  

  At this time, the results of (f (g 3)) and (f 3) are the same, achieving a mathematical effect.
  Furthermore, C does not have the characteristics of a functional language 2.

• What are the common functional languages?

  coljure、scala、Haskell。
  

• Why are languages ​​such as python/javascrip not functional languages, because they do not have the characteristics of functional languages ​​2.