I don't understand some parts of the code

Question

I'm trying to understand a code from a programming site. This is not very well explained and I have not found the necessary answers.

So..What does it mean val[0] == '\\'' and x[0] == '\\"' ?

Answer 1

#include <iostream>

int main() {
    char a = '\'';
    std::string b = "\"";
    std::cout << "a=" << a << std::endl;
    std::cout << "b=" << b << std::endl;
    return 0;
}

The out put will be:

a='
b="

As the comments indicate this is the only way escape the ' and " characters. you can ignore [0] as that just indicates it's an array of chars and your accessing the first ones.

Answer 2

As other's have mentioned the backslash is used escape certain characters.

To illustrate why we need escape characters, look at the example below:

if(val[0] == ''' && x[0] == '"'){

}

To a person the intention is clear, but to a compiler this is ambiguous.

The compiler will first try to extract tokens from your program like so:

if => IF

( => (

val => IDENTIFIER

[ => [

0 => INTEGER

] => ]

== => EQ_OP

'' => CONSTANT

'&& x[0] == ' => CONSTANT

"'){} => Here it fails. Either the tokenizer sees the ", tries to match a string literal but the tokenizer prevents having an unescaped single quote in a string, and therefore doesn't match anything... causing an error. Option two, the tokenizer doesn't complain about the unescaped single quote, as " must having a closing ", and therefore does not find a match.