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); } }

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); } }

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 } }

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; 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); } }

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; } 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); } }

输出

0: string: 49

参考区块链入门到实战（31）之Solidity – 第一个程序运行