Why I am not getting desired output for my c++ problem - c++

Question

I am solving a question which states: to change every '?' with 'a' in a string if doesn't contain if won't form consecutive 'a' else substitute with 'b', eg. a?b will be abb and not aab because here 2 a's are consecutive.
My problem is for i = 3 my string should be over- written with 'b ' according to my code it is entering into the desired block but the string does n't gets written with b, but in all the other case where it should be witten with 'a' it get's written .Help me out with these.
You can refer the problem statement from here to for better understanding my problem :https://www.hackerearth.com/practice/algorithms/greedy/basics-of-greedy-algorithms/practice-problems/algorithm/exploring-ruins/
#include <iostream>
using namespace std;
int main() {
string str;
cin >> str;
int n = str.size();
for(int i = 0; i < str.size(); i++) {
if(str[i] == '?') {
if(i == 0) {
if(str[i + 1] == 'a')
str[i] = 'b';
else
str[i] = 'a';
cout << "I am in if" << endl;
} else if(i == n - 1) {
if(str[i - 1] == 'a')
str[i] == 'b';
else
str[i] == 'a';
cout << "I am in if of else if " << endl;
} else {
if(str[i + 1] == 'a' || str[i - 1] == 'a') {
str[i] == 'b';
cout << "I am in if of else " << endl;
} else {
str[i] = 'a';
cout << "I am in else of else " << endl;
}
}
cout << str[i] << endl;
} else
continue;
}
cout << str << endl;
return 0;
}
Given string : ?ba??b
desired output : ababab
my output : aba?ab

Answer 1

It will be a lot easier for you if you would use functions to solve this problem.
bool check_neighbors_for_a(const string &str, size_t place) {
bool result = false;
if (place > 0) { // If there is a char before the current char
result = str[place - 1] == 'a'; // If the previous char is 'a' result become true
}
if (place < str.size() - 1) { // If there is a char after the current char
result = result || str[place + 1] == 'a'; // If the result has become true before this line, result will stay true. Else, result will be true if the next char is equal to 'a'.
// For example: b?a => result = (false || 'a' == 'a')
// For example: a?b => result = (true || 'b' == 'a')
// For example: a?a => result = (true || 'a' == 'a')
}
return result;
}
void replace_questions_by_a(string &str) {
for (size_t i = 0; i < str.size(); i++) {
if (str[i] == '?') {
if (check_neighbors_for_a(str, i)) { // If one of the neighbors is equal to 'a'
str[i] = 'b'; // Place 'b' instead of '?'
} else {
str[i] = 'a'; // Place 'a' instead of '?'
}
}
}
}