solidity和mysql_区块链入门到实战（37）之Solidity – 循环语句
与其他语言类似，Solidity语言支持循环结构，Solidity提供以下循环语句。
while
do ... while
for
循环控制语句：break、continue。
Solidity – while循环
语法
Solidity 中， while循环的语法如下：
while(表达式) {
被执行语句(如果表示为真)
}
示例
pragma solidity ^0.5.0;
contract SolidityTest {
uint storedData;
constructor() public{
storedData= 10;
}
function getResult() public view returns(string memory){
uint a= 10;
uint b= 2;
uint result= a +b;returnintegerToString(result);
}
function integerToString(uint _i) internal pure
returns (string memory) {if (_i ==0) {return "0";
}
uint j=_i;
uint len;while (j !=0) {
len++;
j/= 10;
}
bytes memory bstr=new bytes(len);
uint k= len - 1;while (_i != 0) { // while循环
bstr[k--] = byte(uint8(48 + _i % 10));
_i/= 10;
}returnstring(bstr);
}
}
Solidity – do…while循环
语法
Solidity 中， do…while循环的语法如下：
do {
被执行语句(如果表示为真)
}while (表达式);
注意: 不要漏掉do后面的分号。
示例
pragma solidity ^0.5.0;
contract SolidityTest {
uint storedData;
constructor() public{
storedData= 10;
}
function getResult() public view returns(string memory){
uint a= 10;
uint b= 2;
uint result= a +b;returnintegerToString(result);
}
function integerToString(uint _i) internal pure
returns (string memory) {if (_i ==0) {return "0";
}
uint j=_i;
uint len;while (j !=0) {
len++;
j/= 10;
}
bytes memory bstr=new bytes(len);
uint k= len - 1;
do {// do while循环
bstr[k--] = byte(uint8(48 + _i % 10));
_i/= 10;
}while (_i !=0);returnstring(bstr);
}
}
Solidity – for循环
语法
Solidity 中， for循环的语法如下：
for(初始化; 测试条件; 迭代语句) {
被执行语句(如果表示为真)
}
示例
pragma solidity ^0.5.0;
contract SolidityTest {
uint storedData;
constructor() public{
storedData= 10;
}
function getResult() public view returns(string memory){
uint a= 10;
uint b= 2;
uint result= a +b;returnintegerToString(result);
}
function integerToString(uint _i) internal pure
returns (string memory) {if (_i ==0) {return "0";
}
uint j=0;
uint len;for (j = _i; j != 0; j /= 10) { //for循环的例子
len++;
}
bytes memory bstr=new bytes(len);
uint k= len - 1;while (_i !=0) {
bstr[k--] = byte(uint8(48 + _i % 10));
_i/= 10;
}return string(bstr);//访问局部变量
}
}
Solidity – break与contin
continue – 跳出本次循环，继续执行接下来的循环
break – 跳出循环(或跳出代码块)
break 示例
pragma solidity ^0.5.0;
contract SolidityTest {
uint storedData;
constructor() public{
storedData= 10;
}
function getResult() public view returns(string memory){
uint a= 1;
uint b= 2;
uint result= a +b;returnintegerToString(result);
}
function integerToString(uint _i) internal pure
returns (string memory) {if (_i ==0) {return "0";
}
uint j=_i;
uint len;while(true) {
len++;
j/= 10;if(j==0){break; // break语句跳出循环
}
}
bytes memory bstr=new bytes(len);
uint k= len - 1;while (_i !=0) {
bstr[k--] = byte(uint8(48 + _i % 10));
_i/= 10;
}returnstring(bstr);
}
}
输出
0: string: 3
continue 示例
pragma solidity ^0.5.0;
contract SolidityTest {
uint storedData;
constructor() public{
storedData= 10;
}
function getResult() public view returns(string memory){
uint n= 1;
uint sum=0;while( n < 10){
n++;if(n == 5){continue; //当n的和是5时，跳过n。
}
sum= sum +n;
}returnintegerToString(sum);
}
function integerToString(uint _i) internal pure
returns (string memory) {if (_i ==0) {return "0";
}
uint j=_i;
uint len;while(true) {
len++;
j/= 10;if(j==0){break; //break跳出循环
}
}
bytes memory bstr=new bytes(len);
uint k= len - 1;while (_i !=0) {
bstr[k--] = byte(uint8(48 + _i % 10));
_i/= 10;
}returnstring(bstr);
}
}
输出
0: string: 49