Update boucles_conditions.md (code optimisé)

slides/boucles_conditions.md

@@ -17,7 +17,7 @@ int main() {
   int n = 0;
   scanf("%d", &n);
   int res = 0;
-  for (int i = 0; i <= n; ++i) {
+  for (int i = 1; i <= n; ++i) {
     res += i;
   }
   printf("For = %d, the result is %d\n", n, res);