[solidity] if문/반복문/continue와break/equal (feat.솔리디티깨부수기)

if문

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;

contract lec17 {
    string private outcome = "";
    function inIt5(uint256 _number) public returns(string memory) {
        if(_number ==5){
            outcome = "Yes, it is 5";
            return outcome;
        }
        else {
            outcome = "No, it is not 5";
            return outcome;
        }
    }
    function inIt5or3or1(uint256 _number) public returns(string memory){
        if(_number == 5) {
            outcome = "Yes, it is 5";
            return outcome;
        }
        else if(_number == 3) {
            outcome = "Yes, it is 3";
            return outcome;
        }
        else if(_number == 1) {
            outcome = "Yes, it is 1";
            return outcome;
        }
        else {
            outcome = "No, it is not 5, 3 or 1";
            return outcome;
        }
    }
}

 

 

반복문

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;

//for, while, do-while
contract lec18 {
    event CountryIndexName (uint256 indexed _index, string _name);
    string[] private countryList = ["South Korea", "North Korea", "USA","China","Japan"];

//for문
    function forLoopEvents() public {
        for(uint256 i = 0; i<countryList.length; i++) {
            emit CountryIndexName(i, countryList[i]);
        }
    }

//while문
    function whileLoopEvents() public {
        uint256 i = 0;
        while(i<countryList.length) {
            emit CountryIndexName(i, countryList[i]);
            i++;
        }
    }

//do-while문
    function doWhileLoopEvents() public {
        uint256 i = 0 ;
        do {
            emit CountryIndexName(i, countryList[i]);
            i++;
        }
        while(i<countryList.length);
    }
}

 

 

continue와 break

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;

contract lec19 {
    //continue : 다음 반복문으로 이동
    //break: 반복문을 끝냄
    event CountryIndexName(uint256 indexed _index, string _name);
    string[] private countryList = ["South Korea", "North Korea", "USA", "China", "Japan"];

    function useContinue() public {
        for(uint256 i=0; i<countryList.length; i++){
            if( i%2 == 1 ){ //홀수인경우
                continue; //i++
            }
            emit CountryIndexName(i, countryList[i]); //짝수만출력
        }
    }
    function useBreak() public {
        for(uint256 i=0; i<countryList.length; i++) {
            if(i==2){ //인덱스0,1만출력됨
                break; //2에서종료
            }
            emit CountryIndexName(i, countryList[i]);
        }
    }
}

 

 

equal

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;

contract lec20 {
    event CountryIndexName(uint256 indexed _index, string name);
    string[] private countryList = ["South korea", "North Korea", "USA", "China", "Japan"];

    function linearSearch(string memory _search) public view returns(uint256, string memory){
        for(uint256 i=0; i<countryList.length; i++){
            //솔리디티에는 비교하는 기능이 없다. "aaa"==="aaa", "aa".isEqual("Aa")
            //bytes화해서 keccak256돌려서 같은지 비교하는 방법만 있다!
            if(keccak256(bytes(countryList[i])) == keccak256(bytes(_search))){
                return (i, countryList[i]);
            }
        }
        return(0, "Nothing"); //for문다돌았는데도 없으면 출력...대소문자구별하네???헐...ㅋ
    }
}