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Preconditions

• To use assert() you must #include<cassert>.
• assert() is really a macro - a special instruction to the compiler that inserts complex code into the program.

  double future_value(double initial_balance, double p, int n)
  {
     assert(p >= 0);
     assert(n >= 0);
  
     return initial_balance * pow(1 + p / 100, n);
  }
  

• As a programmer, you must fully document any preconditions that the function must meet. That is, the legal values for function input.

  /**
     Computes the value of an investment with compound interest.
     @param initial_balance the initial value of the investment
     @param p the interest rate in percent; must be >= 0
     @param n the number of periods the investment is held; must be >= 0
     @return the balance after n periods
  */
  

• If a function call does not satisfy the preconditions, the function is free to do anything.
  • Function causes the program to terminate.
  • Return a "safe" default value.

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