diff --git a/qualdev/Td_debug/exercice.ts b/qualdev/Td_debug/exercice.ts
index 7af9ae480a379d18df633e6c344bea15658379ef..8163db18a5e7789f0a82ede904426f502cb8924d 100644
--- a/qualdev/Td_debug/exercice.ts
+++ b/qualdev/Td_debug/exercice.ts
@@ -30,4 +30,15 @@ function deb3(x: number, y: number): void {
 let x = 10;
 let y = 20;
 deb3(x, y);
-console.log(x, y);
\ No newline at end of file
+console.log(x, y);
+
+// exercice4
+function deb4(xy: number[]): void {
+    let tmp = xy[0];
+    xy[0] = xy[1];
+    xy[1] = tmp;
+    console.log(xy);
+}
+let xy = [10, 20];
+deb4(xy);
+console.log(xy);
\ No newline at end of file