first working version of ex13

ex13.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+    if(argc != 2) {
+        printf("ERROR: You need one argument.\n");
+        return 1;
+    }
+
+    int i = 0;
+    for(i = 0; argv[1][i] != '\0'; i++) {
+        char letter = argv[1][i];
+
+        switch(letter) {
+            case 'a':
+            case 'A':
+                printf("%d: 'A'\n", i);
+                break;
+
+            case 'e':
+            case 'E':
+                printf("%d: 'E'\n", i);
+                break;
+
+            case 'i':
+            case 'I':
+                printf("%d: 'I'\n", i);
+                break;
+
+            case 'o':
+            case 'O':
+                printf("%d: 'O'\n", i);
+                break;
+
+            case 'u':
+            case 'U':
+                printf("%d: 'U'\n", i);
+                break;
+
+            case 'y':
+            case 'Y':
+                if (i > 2) {
+                    printf("%d: 'Y'\n", i);
+                }
+                break;
+
+            default:
+                printf("%d: %c is not a vowel\n", i, letter);
+        }
+    }
+
+    return 0;
+}
+