## C++, math, string_fibonacci.cpp

``````/**
* @file
* @brief This Programme returns the Nth fibonacci as a string.
*
* The method used is manual addition with carry and placing it in a string
* which is called string addition This makes it have no bounds or limits
*
* @see fibonacci_large.cpp, fibonacci_fast.cpp, fibonacci.cpp
*/

#include <iostream>
#ifdef _MSC_VER
#include <string>  // use this for MS Visual C
#else
#include <cstring>  // otherwise
#endif

/**
* function to add two string numbers
* \param [in] a first number in string to add
* \param [in] b second number in string to add
* \returns sum as a std::string
*/
std::string add(std::string a, std::string b) {
std::string temp = "";

// carry flag
int carry = 0;

// fills up with zeros
while (a.length() < b.length()) {
a = "0" + a;
}

// fills up with zeros
while (b.length() < a.length()) {
b = "0" + b;
}

// adds the numbers a and b
for (int i = a.length() - 1; i >= 0; i--) {
char val = static_cast<char>(((a[i] - 48) + (b[i] - 48)) + 48 + carry);
if (val > 57) {
carry = 1;
val -= 10;
} else {
carry = 0;
}
temp = val + temp;
}

// processes the carry flag
if (carry == 1) {
temp = "1" + temp;
}

while (temp[0] == '0' && temp.length() > 1) {
temp = temp.substr(1);
}

return temp;
}

/** Fibonacci iterator
* \param [in] n n^th Fibonacci number
*/
void fib_Accurate(uint64_t n) {
std::string tmp = "";
std::string fibMinus1 = "1";
std::string fibMinus2 = "0";
for (uint64_t i = 0; i < n; i++) {
fibMinus2 = fibMinus1;
fibMinus1 = tmp;
}
std::cout << fibMinus2;
}

/** main function */
int main() {
int n;
std::cout << "Enter whatever number N you want to find the fibonacci of\n";
std::cin >> n;
std::cout << n << " th Fibonacci is \n";
fib_Accurate(n);

return 0;
}
``````