Empty string increasing size by one in C++ -

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the following code snippets output different results same input (7747774):

a:

#include <iostream> #include <string> #include <algorithm> using namespace std;  int main() {     string n;     cin >> n;      int k = count(n.begin(), n.end(), '4') + count(n.begin(), n.end(), '7');     string c = to_string(k);     bool lucky = (k>0) && (count(c.begin(), c.end(), '4') + count(c.begin(), c.end(), '7') == c.size());     cout << (lucky?"yes":"no") << endl;       return 0; }

b:

#include <iostream> #include <string> #include <algorithm> using namespace std;  int main() {     string n;     cin >> n;      int k = count(n.begin(), n.end(), '4') + count(n.begin(), n.end(), '7');     string c = "" + k;     bool lucky = (k>0) && (count(c.begin(), c.end(), '4') + count(c.begin(), c.end(), '7') == c.size());     cout << (lucky?"yes":"no") << endl;       return 0; }

a prints yes, while b prints no, size of 'c' in b has increased one. why that?

string c = "" + k;

doesn't think does. think equivalent std::to_string(k), no. actually increment pointer of string literal "" k.

that's undefined behavior (as k not 0 - wouldn't change pointer), , can result. have use std::to_string or std::atoi or similar functions.


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