Update cours_11.md (Fonction void qui retournait un int)

slides/cours_11.md

@@ -216,12 +216,12 @@ void stack_peek(stack s, int *val) {
 . . .
 
 ```C
-void stack_pop(stack *s, int *val) {
+int stack_pop(stack *s, int *val) {
     stack_peek(*s, val);
     element *tmp = *s;
     *s = (*s)->next;
     free(tmp);
-    return val;
+    return *val;
 }
 ```