In our bookstore problem, we’ll have several records that we’ll want to combine into a single total. As a simpler, related problem, let’s look first at how we might add two numbers. Using the IO library, we can extend our main
program to prompt the user to give us two numbers and then print their sum:
#include <iostream>
int main()
{
std::cout << "Enter two numbers:" << std::endl;
int v1 = 0, v2 = 0;
std::cin >> v1 >> v2;
std::cout << "The sum of " << v1 << " and " << v2
<< " is " << v1 + v2 << std::endl;
return 0;
}
This program starts by printing
Enter two numbers:
on the user’s screen and then waits for input from the user. If the user enters
3 7
followed by a newline, then the program produces the following output:
The sum of 3 and 7 is 10
The first line of our program
#include <iostream>
tells the compiler that we want to use the iostream
library. The name inside angle brackets (iostream
in this case) refers to a header. Every program that uses a library facility must include its associated header. The #include
directive must be written on a single line—the name of the header and the #include
must appear on the same line. In general, #include
directives must appear outside any function. Typically, we put all the #include
directives for a program at the beginning of the source file.