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  1. #include <iostream>
  2. #include <fstream>
  3. #include <vector>
  4.  
  5. int main(void)
  6. {
  7. 	auto& datafile = std::cin;
  8.  
  9. 	if (!datafile) {
  10. 	    std::cerr << "Could not open \'foo.txt\', make sure it is in the correct directory." << std::endl;
  11. 	    exit(-1);
  12. 	}
  13.  
  14. 	int num_entries;
  15. 	// this tests whether the number was gotten successfully
  16. 	if (!(datafile >> num_entries)) {
  17. 	    std::cerr << "The first item in the file must be the number of entries." << std::endl;
  18. 	    exit(-1);
  19. 	}
  20.  
  21. 	// here we range check the input... never trust that information from the user is reasonable!
  22. 	if (num_entries < 0) {
  23. 	    std::cerr << "Number of entries cannot be negative." << std::endl;
  24. 	    exit(-2);
  25. 	}
  26.  
  27. 	// here we allocate an array of the requested size.
  28. 	// vector will take care of freeing the memory when we're done with it (the vector goes out of scope)
  29. 	std::vector<int> ints(num_entries);
  30. 	int sum = 0;
  31. 	for( int i = 0; i < num_entries; ++i ) {
  32. 	    // again, we'll check if there was any problem reading the numbers
  33. 	    if (!(datafile >> ints[i])) {
  34. 	        std::cerr << "Error reading entry #" << i << std::endl;
  35. 	        exit(-3);
  36. 	    }
  37. 	    sum += ints[i];
  38. 	}
  39.  
  40. 	std::cout << "Read " << num_entries << " numbers having a sum of " << sum << std::endl;
  41. 	return 0;
  42. }
  43.  
Success #stdin #stdout 0s 3432KB
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stdin
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3
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stdout
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Read 3 numbers having a sum of 9
https://ideone.com/0vzPPN
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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