Week 2 Discussion

Written by John Pham

Written / Modified by Josh Beto

Lesson Plan

We will be covering new ways to access the input and output stream this week and going over problem solving

Standard Input and Output (Using a keyboard)

• #include <iostream> to do standard input and output operations

• cout and cin are variables provided by iostream

• Standard Output

  • cout is an ostream object that allows you to use <<, the insertion operator

    • cout will write words to the buffer. The buffer prints to the console when std::flush or std::endl is written.

      •   int x = 6;
        
          cout << x << endl;
          // user types in "hello world"
          // only "hello" is stored in userInput
        

    • Important Note: cout only prints to the console when the buffer is flushed.

• Standard Input

  • cin is an istream object that allows you to use >>, the extraction operation

    • cin will only fetch “words” from the buffer. It will stop at whitespaces and newlines.

      • string userInput;
        
        cin >> userInput;
        // user types in "hello world"
        // only "hello" is stored in userInput
        

  • getline() is a function that reads a “line of words” from the buffer

    • string userInput;
      
      getline(cin, userInput);
      //user types in "hello world"
      // "hello world" gets stored in userInput
      

File Input and Output

We can also use files as input for our programs and write to files rather than to the screen. We can accomplish this by using file streams.

• #include<fstream> to do file input and output operations
• File Input
  • You need to instanstiate a ifstream object
    • ifstream inputFileStream;
  • To open a file, you will use the open() method
    • inputFileStream.open("myTextFile.txt")
  • You can check if the file opened properly by using the is_open() method

    • if (inputFileStream.is_open()) {
        cout << "File opened successfully!" << endl;
      }
      else {
        cout << "File failed to open" << endl;
      }
      

  • Once you have a file open, you can read from the from by using the extraction operator
    • inputFileStream >> myVar
  • When you’re done reading from a file, it’s good practice to close the stream by using the close() method
    • inputFileStream.close()
• File Output
  • You need to instanstiate a ofstream object
    • ofstream outputFileStream
  • You can then create a new file by using the open() method
    • outputFileStream.open("output.txt");
  • You can check if the file was created using the is_open() method
    • outputFileStream.is_open() ? cout << "File opened" : "File failed to open";
  • You can write to the file using the insertion operator
    • outputFileStream « “This text will be written to the file” « endl;

Operators

• You can think of operators as a special kind of function
• Operators take in a set of arguments and may return a value
• Take the + operator as an example:

  int main() {
    int x = 3 + 2; // '+' operator takes in arguments '3' and '2', adds them, and returns '5'
    return 0;
  }
  

• Like functions, operators can also be overloaded

  /*  In this example, the '<<' operator takes in multiple types. This is how
    you are able to use cout << *type* with many different types from 'int' to 'double'! 
  */
  ostream& operator<< (bool val);
  ostream& operator<< (int val);
  ostream& operator<< (double val);
  

• Challenge: Why are you able to chain together multiple << or >> respectively?
  • Hint: Look back on what << and >> return and the cin and cout types

Problem Solving Tips

• If you get stuck on a part, skip to the parts you know and abstract the parts you do not know. Abstract means to understand what something does, but not think about how it is done.
• Example: You have a function bool isAcceptable(int x)
• You need to remove elements within a vector<int> v that are considered not acceptable.
  • You can simply call isAcceptable(int x) to check for which elements to remove even if you do not know how to write bool isAcceptable(int x)

Mini Quiz

• Part 1: Write a function to calculate the digital root of a number. The definition of a digital root can be found here: https://en.wikipedia.org/wiki/Digital_root
• Part 2: Implement the following function: highestRoot(const vector<int> &v). This function returns the number within v with the highest digital root. Assume v is nonempty.
• Part 3: Write a main that generates 10 random integers from range 10-999 and prints the integer with the highest digital root among them.