How to assign char to string object in c++?

Question

i am trying to convert the string into capital letter string by assigning single char's to string like this:-

#include <iostream>
#include <string>
#include <cstring>
#include <cctype>
using namespace std;

int main()
{
  string a;
  getline(cin,a);
  string b;
  b.reserve(a.size()+1);
  for(int i=(a.size()),i1=0;1;i1++)
  {
    if(b[i1]!='\0')
        b[i1]=(char)toupper(a[i1]);
    else
    {
        a[i1]='\0';
        break;
    }
  }
  cout << b <<endl;
}

every when run a.out by ./a.out ,Only endl gets prints

here is sample run:-

$ ./a.out 
play clash royale

$ 

What is wrong in my program?? How can I assign single char to string??

Answer 1

There are some issues with your program. The main one is probably the diference between string reserve and string resize. What you want in your program is already had a string of a.size() length, so, use b.resize(a.size()).

A working version is bellow (there are better ways to write this, just being most consistent with OP proposal):

#include <iostream>
#include <string>
#include <cstring>
#include <cctype>
using namespace std;

int main()
{
   string a;
   getline(cin,a);
   string b;
   b.resize(a.size());
   for(int i1=0; i1 < a.size();i1++)
   {
      if(a[i1]!='\0')
          b[i1]=(char)toupper(a[i1]);
      else
      {
          b[i1]='\0';
          break;
      }
   }
   cout << b <<endl;
}