Reverse a string. Not sure why this logic is wrong. C++ - c++

Question

I am a beginner in solving algorithmic questions. Until now, I have only self-taught coding. So, I am not sure about the proper conventions.
I was trying to solve a question to reverse a string.There is some problem with the code but I am not sure what it is after debugging step-by-step.
class Solution {
public:
string reverseString(string s) {
int n = s.length();
string reverse;
for (int i=0;i<s.length();i++)
{
reverse[i] = s[n-1];
n=n-1;
}
return reverse;
}
};
Input: "Hello"
Output needed: "olleh"
My output: "olleh " (extra space)
Input: A man, a plan, a canal: Panama
Output: No output
I searched online for solutions. There were related to pointers. It would be great if someone helped me understand why this logic doesn't work and why using pointers is a better idea.
ALREADY GIVEN. CANNOT CHANGE:
string stringToString(string input) {
assert(input.length() >= 2);
string result;
for (int i = 1; i < input.length() -1; i++) {
char currentChar = input[i];
if (input[i] == '\\') {
char nextChar = input[i+1];
switch (nextChar) {
case '\"': result.push_back('\"'); break;
case '/' : result.push_back('/'); break;
case '\\': result.push_back('\\'); break;
case 'b' : result.push_back('\b'); break;
case 'f' : result.push_back('\f'); break;
case 'r' : result.push_back('\r'); break;
case 'n' : result.push_back('\n'); break;
case 't' : result.push_back('\t'); break;
default: break;
}
i++;
} else {
result.push_back(currentChar);
}
}
return result;
}
int main() {
string line;
while (getline(cin, line)) {
string s = stringToString(line);
string ret = Solution().reverseString(s);
string out = (ret);
cout << out << endl;
}
return 0;
}

Answer 1

As you create reverse, you have to pass the length of the string as an argument, else the created string will be of size 0. This could look like this:
string reverseString(string s) {
int n = s.length();
string reverse(n,'0');
for (int i=0;i<s.length();i++)
{
reverse[i] = s[n-1];
n=n-1;
}
return reverse;
}

Answer 2

Reversing a string is trivial. Just construct a new one from the reverse iterators:
std::string reverse_str(s.rbegin(), s.rend());
or
std::string reverse_str(s.crbegin(), s.crend());
Here's how I would write your function:
string reverseString(const string& s) {
return {s.crbegin(), s.crend()};
}

Answer 3

Try this out
class Solution {
public:
string reverseString(string s) {
//cout<<"inside func";
int n = s.length();
cout<<n<<endl;
char reverse[sizeof(char)*n];// reverse stores the reverse of original string s
int i= 0;
for ( i=0;i<s.length();i++)
{
reverse[i] = s[n-i-1];
}
return reverse;
}
}
int main()
{
string s,r;
Solution sol;
s= "hello";
r= sol.reverseString(s);
cout<<r<<endl;
cout<<r.length()<<endl;
return 0;
}
when i= 0, n-i-1= n-1 which is the last element of the original string s. So the first element of the reverse string is the last element of s. Next i becomes i+1 i.e 1. This time second element of the reverse string is the last but one element in string s. This procedure is repeated till i < s.length(). The element to get copied is for index i= n-1 and n becomes n-(n-1)-1= 0, so the last element of reverse string is the first element of s. After this the loop exists. No additional extra characters are added.