fix scan.c for ID accept non-alphabet characters and resolve some warning

src/main.c

@@ -45,7 +45,7 @@ int TraceCode = FALSE;
 
 int Error = FALSE;
 
-main(int argc, char *argv[]) {
+int main(int argc, char *argv[]) {
     TreeNode *syntaxTree;
     char pgm[120]; /* source code file name */
     if (argc != 2) {

src/scan.c

@@ -219,7 +219,6 @@ TokenType getToken(void) { /* index for storing into tokenString */
                     currentToken = ERROR;
                 }
                 break;
-
             case INLT:
                 state = DONE;
                 if (c == '=') {
@@ -249,7 +248,7 @@ TokenType getToken(void) { /* index for storing into tokenString */
                 }
                 break;
             case INID:
-                if (!isalpha(c)) { /* backup in the input */
+                if (!isalnum(c)) { /* backup in the input */
                     ungetNextChar();
                     save = FALSE;
                     state = DONE;

src/util.c

@@ -156,7 +156,7 @@ char *copyString(char *s) {
 /* Variable indentno is used by printTree to
  * store current number of spaces to indent
  */
-static indentno = 0;
+static int indentno = 0;
 
 /* macros to increase/decrease indentation */
 #define INDENT indentno += 2