How do I read a string char by char in C++?

Question

I need to read a string char by char in order to perform some controls on it. Is it possible to do that? Have I necessarily got to convert it to a char array? I tried to point at single chars with string_to_control[i] and then increase i to move, but this doesn't seem to work. As an example, I post a piece of the code for the control of parenthesis.

bool Class::func(const string& cont){
    const string *p = &cont;
    int k = 0;
    //control for parenthesis
    while (p[k].compare('\0') != 0) {
        if (p[k].compare("(") == 0) { ap++; };
        if (p[k].compare(")") == 0) { ch++; };
        k++;
    };
    //...
};

The string is copied alright, but as soon as I try the first comparison an exception is thrown.

EDIT: I add that I would like to have different copies of the initial string cont (and move on them, rather than on cont directly) in order to manipulate them (later on in the code, I need to verify that certain words are in the right place).

Answer 1

The simplest way to iterate through a string character by character is a range-for:

bool Class::func(const string& cont){
    for (char c : cont) {
        if (c == '(') { ap++; }
        if (c == ')') { ch++; }
    }
    //...
};

---

The range-for syntax was added in C++11. If, for some reason, you're using an old compiler that doesn't have C++11 support, you can iterate by index perfectly well without any casts or copies:

bool Class::func(const string& cont){
    for (size_t i = 0; i < cont.size(); ++i) {
        if (cont[i] == '(') { ap++; }
        if (cont[i] == ')') { ch++; }
    }
    //...
};

Answer 2

If you just want to count the opening and closing parentheses take a look at this:

bool Class::func(const string& cont) {
    for (const auto c : cont) {
        switch (c) {
            case '(': ++ap; break;
            case ')': ++ch; break;
        }
    }
    // ...
}