Binary to Decimal

#include <iostream>
#include <fstream> // For File I/O
#include <string>

using namespace std;

bool validate_line(string s);
int  bin_to_dec(string s);
void pretty_print_line(string s);

int main(void) 
{
  ifstream inFile; // Data file

  // Promts the user for a file name. 
  string fileName; // File name 
  string binary; 

  cout << "Input file name: "; 
  cin >> fileName; 

  // Opens the File. 
  inFile.open(fileName.c_str()); // Changes variable into a C string and opens the file. 
  if (!inFile.good()) {
    cerr << "Could not open " << fileName << endl << endl;
    return 1;
  }

  cout << endl << "Binary Number\tDecimal Equivalent" << endl; 

  while (!inFile.eof()) {
    string s_line;
    getline(inFile, s_line); // Read a complete line.

    if (!inFile.eof()) {
      // Now make sure there are no invalid characters.
      if (!validate_line(s_line)) {
        cerr << "Line " << s_line << " contains invalid characters! " << endl;
      } else {      
         // Compute the result
         pretty_print_line(s_line);
         cout << "\t\t" << bin_to_dec(s_line) << endl;
      }
    }
  }

  return 0;
}

bool validate_line(string s) 
{
  const char *ptr;
  
  // Go through the string and check for invalid chararacters
  for (ptr = s.c_str(); *ptr; ptr++) 
    if (*ptr != '0' && *ptr != '1' && *ptr != ' ') // Spaces are valid chars
      return false;
  
  return true;
}

int bin_to_dec(string s) 
{
  int n_len = s.size(); // Compute initial length of string;
  int n_count = 0;
  int n_pow;
  int n_retval = 0;

  // First eliminate the leading spaces before the line
  for (int i = 0; i < s.size(); i++, n_count++)
    if (s[i] != ' ')
      break;

  // Now compute the actual string length (minus the leading spaces)
  n_len -= n_count;

  // Now compute the multiplying factor
  n_pow = 1 << (n_len - 1);

  // Now compute the result
  char ch;
  for (int i = n_count; i < s.size(); i++) {
    ch = s[i];     // Get the char at position i
    if (ch == '1') // If the char is '1' ....
      n_retval += n_pow; // ... add power of 2 to it (n_pow * 1 = n_pow)

    n_pow >>= 1; // Divide multiplying factor by 2 each time
  }
  return n_retval;
}

void pretty_print_line(string s) 
{
  // Print the line without the leading spaces
  for (int i = 0; i < s.size(); i++) 
    if (s[i] != ' ')
      cout << s[i];
}

        1
       10a
     1001
1100
1101
10001

// binarytoint.cpp : Defines the entry point for the console application.
//
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main(int argc, char* argv[]) {
	ifstream inFile; // Data file

	// Promts the user for a file name. 
	string fileName; // File name 
	string binary; 

	cout << "Input file name: "; 
	cin >> fileName; 

	// open the file
	inFile.open(fileName.c_str() );

	// make sure the file is valid
	if (!inFile.good()) {
		cerr << "Could not open file: " << fileName << endl;
		return -1;
	}	

	// print out the output header
	cout << "Binary\tDecimal" << endl;

	// loop through each line of the file
	while(!inFile.eof()) {
		string in_str;
		int pos = 0;
		unsigned int val = 0;  // I assume the values are all > 0
		bool isValid = true;
		
		// get a line 
		getline(inFile, in_str);
		
		// go past the leading spaces if any
		for(pos; pos < in_str.length(); pos++)
			if(in_str[pos] != ' ')
				break;
	
		// loop through each character in the line now
		for(pos; pos < in_str.length(); pos++) {

			// make sure the value is a one or zero, if neither set the valid flag
			// to false and break out of the loop
			if(in_str[pos] != '0' && in_str[pos] != '1') {
				isValid = false;
				break;
			}

			// use a binary shift operator to move the bits one to the left
			val = val << 1;
			if (in_str[pos] == '1')  // if the value is a one, add a bit to the rightmost part
				val = val | 1;		 // of the integer
				
		}
		
		// if we are at the end of the file, don't print
		if (!inFile.eof())
			if(isValid) // remember the valid flag? use it here to print out the proper message
				cout << in_str << '\t' << val << endl;
			else
				cout << in_str << "\tis not a valid binary number" << endl;
	}

	// make sure to clean up after ourselves
	inFile.close();


	return 0;
}