Processing strings with toupper() causing an infinite loop - c++

Question

I'm trying to write a program to convert one letter of each word to uppercase. argv[1] is a number like 3. If argv[1] is 3, only the third letter of each word should be uppercase and the others lowercase.
I wrote this disaster of a code, and it's stuck in an infinite loop that only displays the first input char repeatedly.
I need help with the logic.
#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;
int main(int argc, char *argv[])
{
int c; // yes, read chars in as ints.
int ncounter = atoi(argv[1]);
int cchecker = 0;
c = cin.get();
while (!cin.eof())
{
if (c == ' ')
{
cchecker = 0;
}
else
{
if (cchecker == ncounter)
{
c = (toupper(c));
cchecker++;
}
else
{
c = (tolower(c));
cchecker++;
}
}
cout.put('\n'); // sometimes this is needed: you'll know when
}
}
Update here's new code, it works almost perfect, except it sometimes doesn't uppercase the first word, kinda strange.
#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;
int main (int argc, char *argv[])
{
int c ; // yes, read chars in as ints.
int ncounter = atoi(argv[1]);
int cchecker = 0;
c = cin.get() ;
while (!cin.eof())
{
if (c == ' ')
{
cchecker = 0;
cout.put (c);
c = cin.get ();
cchecker++;
}
else
{
if (cchecker == ncounter)
{
cout.put (toupper(c));
c = cin.get() ;
cchecker++;
}
else
{
cout.put (tolower(c));
c = cin.get() ;
cchecker++;
}
}
}
cout.put('\n') ; // sometimes this is needed: you'll know when
}

Answer 1

while (!cin.eof())
Your loop condition states, that the loop ends if eofbit of the standard input stream (represented by the std::cin object) was set in the last iteration. Eofbit would be set upon reading from the standard input when there is no more characters there.
it's stuck in an infinite loop
Your loop never reads from the standard input, and therefore the state of the loop condition can never change. If the loop is entered, it will never stop.

Answer 2

As others have stated, you are reading from std::cin only one time, before entering the loop, so you get stuck in an infinite loop because you never call cin.get() again inside the loop so cin.eof() has a chance to change value. Though, you should consider using while (cin.get(ch)) instead of while (!cin.eof()).
But, why are you reading from std::cin one char at a time to begin with? You say you want to change letters in words, so you should be reading whole words, not individual characters.
Try using operator>> in a loop to read a whole word, replacing the Nth char in that word, eg:
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cctype>
char my_toupper(char ch)
{
return std::toupper(static_cast<unsigned char>(ch));
}
char my_tolower(char ch)
{
return std::tolower(static_cast<unsigned char>(ch));
}
int main(int argc, char *argv[])
{
int ncounter = std::atoi(argv[1]);
std::string word;
while (cin >> word)
{
std::transform(word.begin(), word.end(), word.begin(), my_tolower);
if (word.size() >= ncounter)
word[ncounter-1] = my_toupper(word[ncounter-1]);
std::cout << word << "\n";
}
return 0;
}