#include <cmath>#include <iostream>#include <unordered_map> struct Node{double x, y;}; int main(){    Node nodes[3]={{1,0},{2,0},{3,0}}; // mag is a map mapping the address of a Node to its magnitude in the planestd::unordered_map<Node*,double> mag={{ nodes+0,1},{ nodes+1,2},{ nodes+2,3}}; // Change each y-coordinate from 0 to the magnitudefor(auto iter= mag.begin(); iter!= mag.end();++iter){auto cur= iter->first;// pointer to Node        cur->y= mag[cur];// could also have used cur->y = iter->second;} // Update and print the magnitude of each nodefor(auto iter= mag.begin(); iter!= mag.end();++iter){auto cur= iter->first;        mag[cur]=std::hypot(cur->x, cur->y);std::cout<<"The magnitude of ("<< cur->x<<", "<< cur->y<<") is ";std::cout<< iter->second<<'\n';} // Repeat the above with the range-based for loopfor(auto i: mag){auto cur= i.first;        cur->y= i.second;        mag[cur]=std::hypot(cur->x, cur->y);std::cout<<"The magnitude of ("<< cur->x<<", "<< cur->y<<") is ";std::cout<< mag[cur]<<'\n';// Note that in contrast to std::cout << iter->second << '\n'; above,// std::cout << i.second << '\n'; will NOT print the updated magnitude}}

The magnitude of (3, 3) is 4.24264The magnitude of (1, 1) is 1.41421The magnitude of (2, 2) is 2.82843The magnitude of (3, 4.24264) is 5.19615The magnitude of (1, 1.41421) is 1.73205The magnitude of (2, 2.82843) is 3.4641