added queen example

slides/exemples/queen.c

+#include <stdio.h>
+#include <stdlib.h>
+
+#define NX 8
+#define NY 8
+
+int main() {
+    char tab[NX][NY];
+    int cx = 4;
+    int cy = 7;
+    for (int i = 0; i < NX; ++i) {
+        for (int j = 0; j < NY; ++j) {
+            if (i == cy || j == cx) {
+                tab[i][j] = '*';
+            } else if (abs(cy - i) == abs(cx - j)) {
+                tab[i][j] = '*';
+            } else {
+                tab[i][j] = ' ';
+            }
+        }
+    }
+    tab[cy][cx] = 'R';
+    for (int i = 0; i < NX; ++i) {
+        for (int j = 0; j < NY; ++j) {
+            printf("%c ", tab[i][j]);
+        }
+        printf("\n");
+    }
+}