Update rand.rst

docs/rand.rst

@@ -33,15 +33,15 @@ The function prototype is `function rand() returns (uint)`. When calling `rand()
 - The `Counter` will automaticlly increase after the `opRand` is called.
 
 
-The developers should be aware of the usage of random number. See `getPureRandnum()` in following example. The return value of `getPureRandnum()` may be the same, because of the following limitation:
+The developers should be aware of the usage of random number.
 
 1. `Randomness Seed` depends on current block. It will be the same until receiving the next block.
 
-2. `Nonce` depends on the transaction order. When you test in local environment and don;t produce a new transaction, you might get the same nonce.
+2. `Nonce` depends on the transaction order. When you test in local environment and don't produce a new transaction, you might get the same nonce.
 
 3. `CodeHash` will not change after you deployed the contract.
 
-4. `Counter` depends on the the called time of rand(). If you call `rand()` twice in same code block, you will receive different results. On the other hands, if you call `getPureRandnum()`, the `rand()` is called on different code block, you may receive the same result.
+4. `Counter` depends on the the called time of rand(). If you call `rand()` twice in same code block, you will receive different results.
 
 Example 1
 ---------
@@ -56,8 +56,7 @@ Example 1
       randnum = rand();
       return randnum;
     }
-    function getPureRandnum() public pure returns (uint) {
-      return rand();
-    }
   }
 
+> You should NOT call `rand()` in a `view` or `pure` function. If the random number does not need to be recorded on the blockchain (i.e., outside of a transaction in a `view` function executed on a single node), it does not need to be generated by the blockchain. The calling application should simply generate a random number locally -- it is much cheaper in terms of resource consumption.
+