prog_2_ getNumberFromUser_dox.txt

/**
 @brief Gets the user to pick a number
 @sideeffect Prompts the user to enter a number
 @returns The number the user entered
 
 This function scans the user's input into a local variable,
 and then returns the value stored in that variable to the calling code.
 */

prog_2_ANSWER_declare.txt

/**
 @brief The answer that the trick always comes up with
 
 For not-very-mysterious algebraic reasons, this trick will always come up
 with the same answer. Rather than have '2' randomly show up in our code as
 a 'magic number', we give it a name here.
 */

prog_2_pause_dox.txt

/**
 @brief Pause until the user is ready to continue
 @sideeffect Prompts the user to press enter
 
 After printing a prompt, this function calls the getchar function
 which will scan for the next letter in the stream. If the user presses
 enter, a newline will be the next character, getchar will finish, and
 the rest of the program will continue.
 */

prog_2_trickCheckArithmetic_dox.txt

/**
 @brief Walk the user through the arithmetic in the trick
 @param theUsersNumber Whatever number the user picked
 @sideeffect Displays the computations for each step of the trick.
 @returns the result of going through the arithmetic of the trick
 
 Displays values of 2^k for the various k, and
 Walks through subtracting 2^0, multiplying by 2^2, adding 2^3, dividing by 2^1,
 and then subtracting twice the original number.
 */

prog_2_trickInstructions_dox.txt

/**
 @brief Walk the user through the steps of the trick
 @sideeffect Displays the instructions for each step of the trick, pausing between steps.
 
 Instructions are:
 Subtract 2^0, multiply by 2^2, add 2^3, divide by 2^1,
 then subtract twice the original number.
 */

prog_2_twice_dox.txt

/**
 @brief Double a number
 @param n The number to double
 @sideeffect None
 @returns Twice n
 
 Very simple function, should just return 2*n or n+n
 */

prog_2_twoToThe_definition.c

int twoToThe(int exponent)
{
    int theResult;
    
    printf("-> Calling twoToThe(%d)\n",exponent);
    
	if(exponent<0) theResult=1/twoToThe(-exponent);
	else if(exponent==0) theResult=1;
	else theResult=twice(twoToThe(exponent-1));
    
    printf("<- twoToThe(%d) returns %d\n",exponent, theResult);
    
    return theResult;
}

prog_2_twoToThe_dox_and_declare.c

/**
 @brief Compute a power of 2
 @param exponent The exponent: how many times to multiply 2 by itself.
 @sideeffect None
 @returns 2^n
 
 This works by using the fact that 2^n is twice 2^(n-1), and 2^0 is 1
 So, if the user gives 0 for n, this just returns n
 Otherwise, it returns twice the value of twoToThe(n-1)
 [We'll talk about this 'recursion' trick later in the class. It's very useful.]
 */
int twoToThe(int exponent);