Implement input validation for leading zero

Add validation to prevent input starting with 0.

infolabs/procmemorylearning/code.c

@@ -62,6 +62,13 @@ int scan(void){
             continue;
         }
         
+        if(x=='0'&&n<=0){
+            while((x = getchar())!='\n')
+                if(x == EOF) return 0;
+        printf("You num cannot starts with 0. Try again\nNum: ");
+        continue;
+        }
+
     }
     if (x == EOF) return 0;
     return(n);