Как исправить string subscript out of range?

#include <iostream>
#include <string>

using namespace std;

string codeNormalization(string code) {
	string result;
	for (int i = 0; i < code.size(); i++) {
		if (code[i] == '\n') {
			result += "\\n";
		}
		else if (code[i] == '"') {
			result += '\'';
		}
		else if (code[i] == '\t') {
			result += "\\t";
		}
		else {
			result += code[i];
		}
	}
	return result = R"("exec(''')" + result + "''')" + R"(")";
}

string myOBF(string codeLine) {
	string result;
	for (int i = 0; i < codeLine.capacity(); i++) {
		int _ord = (int)codeLine[i];
		if (codeLine[i] == codeLine[-1]) {
			result += "chr(" + to_string(_ord) + "))";
		}else if (codeLine[i] == codeLine[0]){
			result += "exec(chr(" + to_string(_ord) + ")+";
		}else {
			result += "chr(" + to_string(_ord) + ")+";
		}
	}
	return result;
}

int main() {
	string code = "print('txt')";
	cout <<myOBF(codeNormalization(code)) << endl;
	system("pause");
}