pre and post condition in function

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 5 Try This page 166
Using std_lib_facilities.h by Bjarne Stroustrup.

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 5 Try This page 166

#include "std_lib_facilities.h"

int area(int length, int width) {
if (length <= 0 || width <= 0) {
error("area() pre-condition");
}

int a = length * width;

if (a <= 0) {
error("area() post-condition");
}
return a;
}

int main()
try
{
int area1;
area1 = area(60000, 60000);
cout << area1;

keep_window_open("x");
}
catch (exception& e) {
cerr << "error: " << e.what() << ‘\n’;
keep_window_open();
return 1;
}
catch (…) {
cerr << "Unknown exception!\n";
keep_window_open();
return 2;
}
[/code]

Output:
High temperature: 42.6
Low temperature: -26.1
Average temperature: 9.28333