update general/build/smart-contracts/gas-optimization, regarding the …

…issue Conflux-Chain#454

docs/general/build/smart-contracts/gas-optimization/constant.md

@@ -1,3 +1,7 @@
+---
+displayed_sidebar: generalSidebar
+sidebar_position: 1
+---
 # Constant vs Immutable
 
 1. `constant`: Declares a constant that must be initialized at the time of declaration and cannot be altered thereafter.

docs/general/build/smart-contracts/gas-optimization/memoryAndCalldata.md

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+---
+displayed_sidebar: generalSidebar
+sidebar_position: 2
+---
+# Memory vs Calldata 
+
+1. `memory`: Typically used for function parameters and temporary variables within functions. Stored in memory and not persistent on the blockchain.
+
+2. `calldata`: Similar to memory, stored in memory and not persistent on the blockchain. The key difference is that calldata variables are immutable and commonly used for function parameters.
+
+Below, we demonstrate how to write data using both `calldata` and `memory` 
+
+```solidity
+contract CalldataAndMemory {
+    struct Confi {
+        uint16 age;
+        string name;
+        string wish;
+    }
+
+    Confi John;
+    Confi Jane;
+
+    function writeToJohn(Confi calldata JohnData) external {
+        John = JohnData;
+    }
+
+    function writeToJane(Confi memory JaneData) external {
+        Jane = JaneData;
+    }
+}
+```
+
+Recommendations for gas optimization:
+
+🌟 In practical situations, if it's possible to use calldata, it is recommended to use `calldata` instead of `memory`.