[Dev-C++] Visual C++

I'm sorry. i know this really simple, but can someone tell what is wrong with this code
   
   
   
  #include <ctype.h>
  #include <fstream>
  int main()
  {
  ifstream infile("input.txt");
  ofstream outfile("ouput.txt");
  string line;
  while (getline(infile,line))
  {
  for (int i=0; i<line.length(); i++)
  
  if (i==0 || line[i-1] == ' ' && isalpha(line[i]))
  line[i] = toupper(line[i]);
  outfile << line << endl;
  }
   
  }
   
   
   
   
   
   
  ERROR:
   
  error C2065: 'ifstream' : undeclared identifier

       
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