solidity智能合约[20]-动态二维数组

function getLength() view public returns(uint){

     return grade.length;
 }

   function getLength3() view public returns(uint){

     return grade[0].length;
 }

function changeLength() public{

      grade.length = 4;

  }

   function changeLength3() public{
      grade.length =2;
  }

    function changeLength4() public{
     grade[0].length =3;
  }
     function changeLength5() public{
     grade[0].length =1;
  }

function changeContent() public{
     grade[1][0] = 100;
 }

 function changeContent2() public{
    grade.push([100,90]);
 }

//获取内容并求和
function   add() view public returns(uint){
    uint sum = 0;
    for(uint i = 0;i<3;i++){
        for(uint j = 0;j<2;j++){
             sum+= grade[i][j];
        }
    }
    return sum;
}