Using to upper incorrectly? Working code until I entered toupper

Question

My program worked like it was supposed to until I added the toupper part into my program. I've tried looking at my error code but it's not really helping. The errors are:

no matching function to call 2 arguments expected, one provided

So I know the error is in those two statements in my while loop. What did I do wrong?

I want to make a name like

john brown go to John Brown

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
using namespace std;

int main(){

  string firstname[5];
  string lastname[5];
  ifstream fin( "data_names.txt" );
  if (!fin) {
    cout << "There is no file" << endl;
  }
  int i = 0;
  while( i < 5 && (fin >> firstname[i]) && (fin >> lastname[i]) ) {
    firstname[0] = toupper(firstname[0]);
    lastname[0] = toupper(lastname[0]);
    i++;
  }
  cout << firstname[0] << " " << lastname [0] << endl;
  cout << firstname[1] << " " << lastname [1] << endl;
  cout << firstname[2] << " " << lastname [2] << endl;
  cout << firstname[3] << " " << lastname [3] << endl;
  cout << firstname[4] << " " << lastname [4] << endl;

  return 0;
}

Answer 1

std::toupper works on individual characters, but you are trying to apply it to strings. Besides adding #include <cctype>, you need to modify your while loop's body:

firstname[i][0] = toupper(firstname[i][0]);
lastname[i][0] = toupper(lastname[i][0]);
i++;

Then it should work as expected. Live demo here

As M.M helpfully pointed out in the comments, you should also check that your strings aren't empty before accessing their first characters, i.e. something like

if (!firstname[i].empty()) firstname[i][0] = toupper(...);

is strongly recommended.

Mind you, you will probably need more sophisticated logic if you get names like McDonald :)

Answer 2

You need ctype.h to get the proper definition for toupper(). It is usually implemented not as a function, but an array mapping.

 #include <ctype.h>

---

The program has several flaws: using a string array instead of a string, not iterating through the string correctly, not declaring but using the C definition of toupper(), not exiting when the file does not exist.

Use this instead:

#include <ctype.h>
#include <iostream>
#include <string>
using namespace std;

int main ()
{
  ifstream fin ("data_names.txt");
  if (!fin) 
  {
    cerr << "File missing" << endl;
    return 1;
  }
  // not sure if you were trying to process 5 lines or five words per line
  // but this will process the entire file
  while (!fin.eof())
  {
       string s;
       fin >> s;
       for (i = 0;  i < s.length();  ++i)
            s [i] = toupper (s [i]);
       cout << s << endl;
  }
  return 0;
}