Solidity Remix simple questions

Question

Am new to Solidity here, this is the code I am testing and remix spits out

browser/Untitled.sol:1:1: : Source file does not specify required compiler version!Consider adding "pragma solidity ^0.4.12 contract C { ^ Spanning multiple lines.

Hopefully someone can give some guidance.

contract C {
    function bytes32ToString(bytes32 x) constant returns (string) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint j = 0; j < 32; j++) {
            byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
            if (char != 0) {
                bytesString[charCount] = char;
                charCount++;
            }
        }
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (j = 0; j < charCount; j++) {
            bytesStringTrimmed[j] = bytesString[j];
        }
        return string(bytesStringTrimmed);
    }

    function bytes32ArrayToString(bytes32[] data) returns (string) {
        bytes memory bytesString = new bytes(data.length * 32);
        uint urlLength;
        for (uint i=0; i<data.length; i++) {
            for (uint j=0; j<32; j++) {
                byte char = byte(bytes32(uint(data[i]) * 2 ** (8 * j)));
                if (char != 0) {
                    bytesString[urlLength] = char;
                    urlLength += 1;
                }
            }
        }
        bytes memory bytesStringTrimmed = new bytes(urlLength);
        for (i=0; i<urlLength; i++) {
            bytesStringTrimmed[i] = bytesString[i];
        }
        return string(bytesStringTrimmed);
    }     }

Answer 1

Include a version pragma at the very top of the source file to get rid of the warning.

pragma solidity ^0.4.0;

contract MyContract {

}

From Solidity documentation:

Version Pragma

Source files can (and should) be annotated with a so-called version pragma to reject being compiled with future compiler versions that might introduce incompatible changes. We try to keep such changes to an absolute minimum and especially introduce changes in a way that changes in semantics will also require changes in the syntax, but this is of course not always possible. Because of that, it is always a good idea to read through the changelog at least for releases that contain breaking changes, those releases will always have versions of the form 0.x.0 or x.0.0.

The version pragma is used as follows:

pragma solidity ^0.4.0;

Such a source file will not compile with a compiler earlier than version 0.4.0 and it will also not work on a compiler starting from version 0.5.0 (this second condition is added by using ^). The idea behind this is that there will be no breaking changes until version 0.5.0, so we can always be sure that our code will compile the way we intended it to. We do not fix the exact version of the compiler, so that bugfix releases are still possible.

Answer 2

As everyone mentioned above, you need to specify the compiler version in the first line of the solidity code:

pragma solidity ^0.4.0;