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;
return integerToString(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;
}
return string(bstr);
}
}
可以参考Solidity – 第一个程序中的步骤,运行上述程序。
输出
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;
return integerToString(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);
return string(bstr);
}
}
可以参考Solidity – 第一个程序中的步骤,运行上述程序。
输出
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;
return integerToString(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
}
}
可以参考Solidity – 第一个程序中的步骤,运行上述程序。
输出
Solidity – break与continue
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;
return integerToString(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;
}
return string(bstr);
}
}
可以参考Solidity – 第一个程序中的步骤,运行上述程序。
输出
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;
}
return integerToString(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;
}
return string(bstr);
}
}