Print the alphabet letters that are not in the line c++ - c++

Question

So, what I'm trying to do is, open and read a file, but read only the first line. I have already done this part. I have to read each character on that line and then I need to print the alphabet letters that are not found in that line.
Let's say the line was:
a b c D E f G H I j k L M n o
So, I will have to print the letters from p-z, because they are not in the line.
So, how will get the letters that are not in the line?!
This is what I have so far:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
using namespace std;
int main(int argc, char *argv[]){
if(argc < 2){
cerr << "Usage: pangram <filename>" << endl;
return 0;
}
ifstream infile(argv[1]);
if (infile.good() == false){
cerr << "Error opening file[" << argv[1] << "]" << endl;
return 1;
}
char ch;
string line;
int a[26] = {a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z};
int brk = 0;
while(infile.good()){
if(brk == 0) {
getline(infile, line);
for(int i=0; i <= line[i]; i++){
if(isalpha(line[i])) {
if(line[i] == )
cout << line[i] << endl;
}
}
}
brk ++;
if(brk == 1) {
break;
}
}
}

Answer 1

Here's a slightly modified version of your solution. I'm intentionally using a stack allocation of 26 bools instead of bitset so it's easier to comprehend.
bool letter_was_seen[26] = {}; // initialize an array to hold 26 bools (A..Z) all to false
getline(infile, line); // read a line into a string
size_t len = line.size();
for (size_t i = 0; i < len; i++)
{
char ch = ::toupper(line[i]); // convert to upper case
if ((line[i] >= 'A') && (line[i] <= 'Z')) // is it a valid letter A..Z ?
{
letter_was_seen[ch - 'A'] = true; // mark it's place in the array as "seen"
}
}
// now print the letters not seen within the line
for (char i = 'A'; i <= 'Z'; i++)
{
int index = (int)(i - 'A');
if (letter_was_seen[index] == false)
{
cout << i; // print the letter not seen
}
}
cout << endl; // print end of line to flush output

Answer 2

Another possible solution,
#include <deque>
#include <algorithm>
#include <iostream>
using namespace std;
int main() {
deque<char> allChars(26);
iota(allChars.begin(), allChars.end(), 'a');
char readString[] = "test xyz";
for (char& c : readString) {
allChars.erase(remove(allChars.begin(), allChars.end(), c),
allChars.end());
}
cout<<"Not removed: ";
for (char& c : allChars) {
cout<<c<<" ";
}
cout<<endl;
}