Why doesn't remix allow inputs of letters in this code?

Question

Okay, so this code is actually designed to revert when anything but 0, 1, ...9, is entered, but let me explain.

I created this code for general practice. It may not have practical use, but it's intent is to convert a string version of the digits 0 - 9 to the uint version. In testing it, it works perfectly when I enter any string with the characters 0 - 9.

pragma solidity ^0.4.24;

contract ConvertStringToUint {       // This version does not limit the number of bytes in the string to 78.

function stringToUint(string _number) public pure returns(uint) {

    bytes memory strBytes = bytes(_number);

    uint i;
    uint digit;
    uint result;

    for (i = 0; i < strBytes.length; i++) {

        if (strBytes[i] == byte(48))        { 
            digit = 0;
        } else if (strBytes[i] == byte(49)) {
            digit = 1;
        } else if (strBytes[i] == byte(50)) {
            digit = 2;
        } else if (strBytes[i] == byte(51)) {
            digit = 3;
        } else if (strBytes[i] == byte(52)) {
            digit = 4;    
        } else if (strBytes[i] == byte(53)) {
            digit = 5;
        } else if (strBytes[i] == byte(54)) {
            digit = 6;
        } else if (strBytes[i] == byte(55)) {
            digit = 7;
        } else if (strBytes[i] == byte(56)) {
            digit = 8;    
        } else if (strBytes[i] == byte(57)) {
            digit = 9;
        } else {
            revert();
        }

        result = result * 10 + digit;

    }
        return result;
}

}

However, when I add a letter or any other character, I get an error I didn't expect.

For example, if I enter string "324", it returns the uint "324". But if I enter string "3a24", I get the error:

Error encoding arguments: SyntaxError: Unexpected token a in JSON at position 2

This suggests that it is not even allowing me to enter these characters as a string in the first place, which I don't understand because the input parameter is a string.

To further test this, I changed the line else if (strBytes[i] == byte(49)) to else if (strBytes[i] == byte(97)), so that now the character "a" will set digit to 0 and the character "0" should cause an error. Sure enough, entering "0" gives me the error:

... VM error: revert. revert The transaction has been reverted to the initial state.

And even at this point, entering "a" still gives me the error:

.. Unexpected token a in JSON at position 1

I've been through it several times and can't account for these error differences. What is going on?

Answer 1

In Remix, there is a weird, ongoing, bug where you must use quotation marks when you use alpha characters in a string. If the function is expecting a string but you only return numerical characters, it will convert it to a string for you.

So, make sure you are literally typing in "3a24" instead of 3a24.

Your contract will still revert it, based on the code, but at least it would work.