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ballot.sol

pragma solidity 0.4.25;
/*数组类型Demo*/
contract DemoTypes303 {
  /*String数组例子*/
  string[] strArr;
  function add(string str) public {
    strArr.push(str);
  }
  function getStrAt(uint n)  public constant returns (string s){
    string storage tmp = strArr[n];
    return tmp;
  }

  function updateStrAt(uint n, string str)  public {
    strArr[n] = str;
  }

  function deleteStrAt(uint index)  public  {
    uint len = strArr.length;
    if (index >= len) return;
    for (uint i = index; i<len-1; i++) {
      strArr[i] = strArr[i+1];
    }

    delete strArr[len-1];
    strArr.length--;
  }
}

eventFilterTest.sol

pragma solidity ^0.4.25;
contract EventFilterTest {
    constructor() public {
        b = 0x12345678901234567890123456789012;
    }
    event Event(uint indexed a, bytes32 b) ;
     event Event2(uint indexed a, bytes32 b) ;

   function foo(uint a) public {
       b =  bytes32(1);
        emit Event(a, b);
        emit Event2(a, b);
    }
    bytes32 b;
}

EventTest.sol

pragma solidity ^0.4.25;
contract SimpleStorage {
    uint public data;
    // event SetX(address indexed _from, uint value);
    event Set(string label, uint value);
    function set(uint x) public {
        data = x;
        // emit SetX(msg.sender, x);
        // emit Set("#####", x);
    }
}

mem_vs_storage.sol

pragma solidity 0.4.25;

contract C {
    uint[] data1;
    uint[] data2;

    function appendOne() public {
        append(data1);
    }

    function appendTwo() public {
        append(data2);
    }

    function append(uint[] storage d) internal {
        d.push(1);
    }
    function getData1() view public returns(uint[]){
        return data1;
    }
    function getData2() view public returns(uint[]){
        return data2;
    }
}