#include <iostream>
#include <cassert>

// Function declarations
int main();
double tent( double x );

// Function definitions
int main() {
  for ( int k{ -25 }; k <= 25; ++k ) {
    double x{ 0.1*k };

    std::cout << "   tent( " << x << " )\t= " << tent( x ) << std::endl;
  }

  return 0;
}

// double tent( ... )
//
// @author    Douglas Wilhelm Harder
// @date      2020-09-09
// @version   1.0
// 
// @param x    a real number 'x' where 0 <= x <= pi/2
// 
// @returns    The tent-function evaluated at this point
//
// @algorithm
//
// This function is defined as:
//            0        if x <= -1 or x >= 1
//          x + 1      if -1 < x <= 0
//          1 - x      if  0 < x <  1
//
// Exercise:
//    1. What happens if you try to assert
//          assert( 0.0 < x < 1.0 );
//       Does it still compile? Does it still work?
//       Can you determine why this may be the case?
//
//       Hint: 0.0 < x < 1.0 works the same way as
//               a + b + c
//             That is, it calculates (a + b) + c.

double tent( double x ) {
  if ( (x <= -1) || (x >= 1) ) {
    return 0.0;
  } else if ( x <= 0 ) {
    return x + 1.0;
  } else {
    // This assertion will fail only if someone makes a mistake
    // and incorrectly alters the first or second conditions above.
    assert( (x > 0.0) && (x < 1.0) );

    return 1.0 - x;
  }
}