How to get every possible string of n characters in c++? - c++

Question

I know it is possible to use n nested for loops to get the result. This however isn't very flexible. If I wanted to get every string of n+2 characters I would have to write an extra two for loops.
I'm pretty sure I should use a parameter called n_Letters and use some kind of recursion. Any ideas? This is how my code looks right now. It gives all the 3 character combinations.
#include <iostream>
#include <string>
using namespace std;
void StringMaker(){
for(int firstLetter = 97; firstLetter < 123; firstLetter++){
char a = firstLetter;
for(int secondLetter = 97; secondLetter < 123; secondLetter++){
char b = secondLetter;
for(int thirdLetter = 97; thirdLetter < 123; thirdLetter++){
char c = thirdLetter;
cout << a << b << c << endl;
}
}
}
}
int main() {
StringMaker(); // I could add a parameter n_Letters here
}

Answer 1

This is a simple tree traversal problem that can easily be solved using recursion. Using a counter (count) and accumulator (partial) recur on your function for each letter until count is zero then print partial.
#include <iostream>
#include <string>
void StringMaker(int count, std::string partial = "") {
if (count == 0) {
std::cout << partial << '\n';
}
else {
for (char letter = 'a'; letter <= 'z'; ++letter) {
StringMaker(count - 1, partial + letter);
}
}
}
int main() {
StringMaker(3);
return 0;
}
Edit: It seems their are some concerns with my answer regarding memory allocations. If it's a concern for you, consider this alternative solution. Increment the first character if it isn't 'z', otherwise set it to a and repeat with the the second character. Do this until the last character is set from z to a. This acts as a sort of base 26 counter with count digits.
#include <iostream>
#include <string>
void StringMaker(size_t count)
{
std::string data(count, 'a');
size_t i = 0;
do
{
std::cout << data << '\n';
for (i = 0; i < count; ++i)
{
auto & next_char = data[i];
if (next_char < 'z') {
++next_char;
break;
}
else {
next_char = 'a';
}
}
} while (i != count);
}
int main() {
StringMaker(3);
return 0;
}

Answer 2

Here is my just-for-fun solution:
void StringMaker(int n)
{
int base = ('z' - 'a' + 1);
std::string str(n, '\0');
for(int i = 0; i < int_pow(base, n); ++i)
{
for(int j = 0; j < n; ++j)
{
str[n - j - 1] = 'a' + i / int_pow(base, j) % base;
}
cout << str << '\n';
}
}
Suppose we have i written in numerical system with base 26 (from a to z), so increment i with n = 4 give us aaaa, aaab and so on