Basic I/O

Here is a simple C++ program containing some I/O (input/output) statements.

#include <iostream>
using namespace std;
int main()
{
   int number;
   cout << "Please enter a number.";
   cin >> number;
   cout << "You entered: " << number << endl;
   return 0;
}
// end program

Let's breakdown this program, and see what it all means.

• The first two lines, #include <iostream> and using namespace std;   inform the compiler of the location of the namespace, and to include them into our program. The first line is what's known as a preprocessor command. The pound(#) sign followed by include begins every preprocessor command. Any built-in or user-defined header files you wish to use in your program must follow this same syntax.
  Note: Built-in header files are enclosed inside the '<' and '>' marks. Header files you create and bring in to the program are enclosed in quotation marks.

• The next line, int main()   is the start of the statements which will become the executable part of our program. The function name is main, and it returns a value that is of type integer. The function has no parameters, as indicated by the empty parentheses.

• The braces { }   are marks which indicate the beginning and end of a function. In this case, they enclose our main program.

• int number; sets "number" as a variable of type integer.

• cout << "Please enter a number: "; prints text or data on the screen. Anything that is enclosed in quotation marks is to be printed.

• cin >> number; receives data from the keyboard and puts it into the variable specified.
  ** The <iostream> allows us to use cout and cin. **

• The line cout << "You entered: " << number << endl; prints out both a literal string and a variable.
  So, if I entered 5, the output would be: You entered 5

• endl - Specifies the end of the line indicator. The next thing printed will begin on the next line.

• return 0; - this line is there because the return value in our main program was designated as an integer.

• // end program - a single line comment.

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Last modified: Friday, 21-Aug-2020 15:28:13 CST
Copyright 2000 Department of Computer Science, University of Regina.