join can now operate on strings.

added vstrcat, but never used.

util.c

@@ -1,12 +1,39 @@
 #include <string.h>
 #include <stdlib.h>
+#include <stdarg.h>
 
 #include "util.h"
 
-char * strdup(char* s) {
+char * strdup(const char* s) {
     if (s == NULL) return NULL;
     char *d = calloc(strlen (s) + 1, sizeof(char));
     if (d == NULL) return NULL;
     strcpy (d,s);
     return d;
 }
+
+char* vstrcat(int n, ...) {
+    va_list va;
+    
+    char** strings = calloc(n, sizeof(char*));
+    size_t stringLength = 0;
+    
+    va_start(va, n);
+    
+    for(int i = 0; i<n; i++) {
+        strings[i] = va_arg(va, char*);
+        stringLength += strlen(strings[i]);
+    }
+    
+    va_end(va);
+    
+    char* newStr = calloc(stringLength+1, sizeof(char));
+    
+    for(int i = 0; i<n; i++) {
+        strcat(newStr, strings[i]);
+    }
+    
+    free(strings);
+    
+    return newStr;
+}