#include <string>
#include <iostream>
#include <utility>
#include <numeric>
#include <limits>
#include <array>

int main()
{
    std::string s = "cat can run fast";

    std::array<char, std::numeric_limits<char>::max()> xlat;
    std::iota(xlat.begin(), xlat.end(), 0);
    std::swap(xlat['a'], xlat['c']);

    for(char& c: s)
        c = xlat[c];

    std::cout << s << '\n';
}