Test 2 Review

type conversions

• implicit/automatic type conversions
  • one implicit conversion for each argument
• casting (explicit type conversions)
  • AخA

     

    static_cast<new_type>(expression)
  • traditional casting (C-style)
    •  

      (new_type) expression
      
      
       

      new_type (expression)
  • other *_cast operators are available in C++ but will not be covered on this test
• Example:
 
#include <iostream>
using namespace std;
​
void fn(int)
{
    cout << "fn(int)" << endl;
}
​
void fn(double)
{
    cout << "fn(double)" << endl;
}
​
int main()
{
    int arg = 12;
    fn(arg);
​
    fn(static_cast<double>(arg));
    fn(static_cast<double>(12));
​
    fn(double(arg));
    fn((double)arg);
​
    return 0;
}

Streams (File I/O, stringstream)

• We have used stream extraction operator >> and the stream insertion operator << with
   

  cin
  and
   

  cout
• file I/O and
   

  stringstream
  can be used these stream operators
• difference between cout/cin and file I/O is primarily with the object creation
• must open a file before reading/writing:
  ​x

   

  ofstream output; // create file output streams, called out1 and bob

  output.open("outfile1.txt"); // for ofstreams, these calls create

  output << "hello world" << endl;
• check if
   

  open()
  succeeds
•  

  close()
  when finished (
   

  close()
  implicitly called when stream object goes out of scope
• append mode:
   

  output.open("file.txt", ios::app); // open file in append mode
• lecture notes
• Example:
 
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <cstdlib> // EXIT_SUCCESS, EXIT_FAILURE
using namespace std;
​
int from_str(const string &s)
{
    istringstream iss(s);
    int rtn = 0;
    iss >> rtn;
    return rtn;
}
​
int main()
{
    ifstream input("numbers.txt");
    if (!input) {
        // open failed
        cerr << "input file could not be opened";
        return EXIT_FAILURE;
   }
​
    int sum = 0;
    for (string line; getline(input, line);) {
        // be aware that no error checking is done on the input
        // (e.g., non-numeric characters) 
        sum += from_str(line);
    }
​
    ofstream output("output.txt");
    if (!output) {
        cerr << "output file could not be opened";
        return EXIT_FAILURE;
    }
​
    output << "sum: " << sum << endl;
​
    return 0;
}

Stream Formatting

• functions and flags for controlling output formatting
  • E.g.,
     

    width()
    and
     

    setw()
•  

  endl
  is a stream manipulator that prints a newline and flushes the output buffer (e.g., write buffered characters to the screen)
•  

  flush
  causes the output buffer to be flushed to the output device before processing proceeds
• other common formatting features can be found in the leture notes and your assignment #4 code

Pointers

• description of values stored in/read from pointer variables
• declaration syntax
• dereference operator (*), address-of operator (&), subscripting operator ([])
• recall that as with other operators these also have associativity and precedence
• pointer arithmetic
• passing to/from functions
•  

  const

Arrays

• what is an array?
• description of values stored in/read from arrays
• declaration syntax
•  

  *, &, and []
  unary operators
• indexing into arrays
• similarities/differences to pointers
• passing to/from functions
•  

  const

memory allocation with new and delete

• array allocation
• similarities/differences to arrays
• passing allocations to/from functions
•  

  const

algorithms

• given an algorithm written in pseudo-code, convert it to reasonably valid C++ code
• create simple algorithms and write it in pseudo-code
• Example: selection sort
  • input - array of numbers
  • output (result) - input list is sorted
  • steps
    • find smallest number in input array and swap it with the 1st element
    • find 2nd smallest number in input array and swap it with 2nd element
    • repeatedly find ith smallest number in input array and swap it with the ith array element until (i-1)th element is placed