Reddit DailyProgrammer http://www.reddit.com/r/dailyprogrammer/comments/1qwkdz/111113_challenge_141_easy_checksums/

gistfile1.cpp

#include <stdint.h>                                                                                                                                                      
        
#include <iostream>
#include <limits>
#include <string>
#include <vector>
        
using namespace std;
        
void cin_discard_newline() {
  cin.ignore(numeric_limits<streamsize>::max(), '\n');
}       
        
uint16_t fletcher_checksum(const string& word) {
  uint8_t count0 = 0, count1 = 0; 
  for (int i = 0; i < word.size(); ++i) {
    unsigned char c = word[i];
    count0 = (count0 + c) % 255;
    count1 = (count1 + count0) % 255;
  }     
  return (count1 << 8) | count0;
}       
        
int main() {
  // Read in number of lines
  int num_lines;
  cin >> num_lines;
  cin_discard_newline();
  cout << hex;
  vector<string> lines;
  for (int i = 0; i < num_lines; ++i) {
    string line;
    getline(cin, line);
    lines.push_back(line);
  }     
        
  for (int i = 0; i < num_lines; ++i) {
    cout << i + 1 << " " << fletcher_checksum(lines[i]) << endl;
  }     
}       
        
/*      
 * http://www.reddit.com/r/dailyprogrammer/comments/1qwkdz/111113_challenge_141_easy_checksums/
 *      
 * Formal Inputs & Outputs
 * Input Description
 * On standard console input, you will first be given an integer N which ranges
 * inclusively from 1 to 256. After this line, you will receive N-lines of ASCII
 * text. This text will only contain regular printable characters, and will all
 * be on a single line of input.
 * Output Description
 * For each line of input, print the index (starting from 1) and the 16-bit
 * Fletcher's checksum as a 4-digit hexadecimal number.
 * Sample Inputs & Outputs
 * Sample Input
 * 3    
 * Fletcher
 * Sally sells seashells by the seashore.
 * Les chaussettes de l'archi-duchesse, sont-elles seches ou archi-seches ?
 * Sample Output
 * 1 D330
 * 2 D23E
 * 3 404D
 */