vault backup: 2023-11-13 13:50:53

Algo/B1/Séminaire/Chapter 4 - A bit of imperative.md

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+<center><img src="https://gitea.louisgallet.fr/lgallet/epicours/raw/branch/main/Algo/S%C3%A9minaire/assets/unitaire-meme.png " width=auto height=400 /> </center>  
+
+
+## 0.1. Print
+If we want to print something in CAML, we have to use this structure
+
+```Ocaml
+# print_string "Hello World!";;
+Hello! - : unit=()
+
+# print_int ;;
+-: int -> unit = <fun>
+
+(*expression*)
+# print_[type] [things to print];;
+[things to print] -: unit=()
+```
+
+**Difference between compiler and interpreter for print**
+```mermaid
+flowchart LR
+
+A[CAML] -- compile --> B[ ] -- exec --> C[standard output] & D[standard error] ~~~ E(on your terminal)
+```
+```mermaid
+flowchart LR
+
+A[CAML] -- interpreter --> B[standard error] & C[standard output] & D[CAML answer] ~~~ E(in the interpreter interface)
+```
+
+**To print something and create a new line for the CAML evaluation**
+```Ocaml
+# print_endline "toto";;
+toto
+-: unit = ()
+```
+**To just print a newline**
+```Ocaml
+# print_newline();;
+-: unit = ()
+
+(* example *)
+# print_newline(print_int 54);;
+54
+-: unit = ()
+```
+
+## 0.2. Sequence of prints
+To print two things on the same line we have to use this structure
+```Ocaml
+# print_string "The answer is: "; print_int 42;;
+The answer is: 42 -: unit = ()
+
+# 3*2*7; print_string "The answer is : ";;
+The answer is -: unit = () 
+Warning 10 [non-unit-statement]: this expression should have type unit.
+
+# print_string "The answer is: "; 3*2*7;;
+The answer is: -:int = 42
+```
+
+### 0.3.  Print in a function
+```OCaml
+# let print_even n = 
+	if n mod 2 = 0 then
+		print_int n;;
+	(*Caml will automaticaly add the else with a empty value ()*)
+val print_even: int -> unit = <fun>
+
+# print_even 4;;
+4 -: unit = ()
+
+# print_even 7;;
+-: unit = ()
+
+# let ret_even n =
+	if n mod 2 = 0 then
+		n;;
+Error: should have int type (*because of the hidden else*)
+
+# let print_even n = 
+	if n mod 2 = 0 then
+		begin
+			print_int n ;
+			print_newline()
+		end;; (*begin and end used to execute more than 1 function into a if*)
+val print_even : int -> unit = <fun>
+
+# print_even 4;;
+4
+-: unit = ()