Learning Cplusplus

Lecture 1 C++ Input/Output

• Two points of view to a program:

Output Data = Program(Input Data)

Program = Model of a problem domain 
Execution = Simulation of the problem domain

Example

#include <iostream>
using namespace std;
int main() {
  int id;
  float av;
  cout << "Enter the id and the average: ";
  cin >> id >> av;
  cout << "Id " << id << '\n‘; 
  cout << "Average " << av << '\n';
  return 0;
}

Using cin and cout

• cin, cout and cerr are variables, defined in iostream;
• cin refers to the standard input stream; cout refers to the standard output stream; and cerr refers to the standard error (output) stream;
• The default action of the input operator >> is to skip white space before reading the next input item (even in the case of char);
• The operators << and >> associate from the left;
• The value of the expression cin >> id refers to the same input stream, after the vallue assigned to id is removed from the stream.

Example 2

Where a true or false value is expected, an expression such as cin >> val is converted to true, if a value is read into val, and false otherwise

#include <iostream> using namespace std;
int main() {    
   int val, sum = 0;    
   cout << "Enter next number: ";  
   while ( cin >> val ) {	  
       sum += val;	  
       cout << "Enter next number: ";  
   }    
   cout << "Sum of all values: "<<sum<<'\n';  
   return 0;
}

Manipulators

• Used to manipulate the output, #include <iomanip> required.
• Except for setw, a manipulator permanently changes the state of the stream to which it is applied.
• setw sets the width of the output field.
• setfill is used to specify a particular fill character, used to fill the extra space when the field width is greater than the item to be output.
• setprecision is used to specify the number of digits of precision of floating-point numbers.

Example

cout << setprecision(5) << 12.48381344;

// Result 12.484

Example 3

#include <iostream>
#include <iomanip>
using namespace std;
int main() {
	float a = 1.05, b = 10.15, c = 200.87;
	cout << setfill( '*' );
	cout << setw( 10 ) << a << '\n';
	cout << setw( 10 ) << b << '\n';
	cout << setw( 10 ) << c << '\n';
	return 0;
}

Out put

Output

******1.05
*****10.15
****200.87

Input from and output to disk-file

ifstream infile	ofstream outfile
ifstream infile; infile.open(“Asd.dat”); infile >> myvariable; infile.close();	ofstream outfile; outfile.open(“Qwe.xyz”); outfile << “hello” << 5; outfile.close();