what are executable/non-executable statements

1. Multiple Files Revisited • what are executable/non-executable statements • out of the ones below which statements are executable #include <iostream> P=3.14; const double PI=3.14; int myfunc(int); • what is a header file? • what is the difference between the two statements? #include <filename> and #include ”filename.h” • why are programs included in multiple files • what are object files and how are they related to multiple file-program • what is linking?

2. Programmer-Defined Functions II Void Functions, Boolean Functions Program Stack, Call-by-Reference

3. Void Functions • void function – does not return a value, can be used only as a standalone statement • void is specified as return type • return-statement is not necessary; if used, cannot contain expression • frequently void functions are output functions: void show_results(double fard, double celd){ cout << fard << ” degrees Fahrenheit is equivalent to\n” << celd << ” degrees Celsius.\n”; return; // not necessary }

4. Boolean Functions • boolean function – return value is boolean • used to compute a binary decision • idiom – use a boolean function as an expression in a looping or branching construct bool again(void){ cout << "Again: [y/n] "; char answer; cin >> answer; if (answer == 'y') return true; else return false; } int main(void){ do cout << "Hello, World!\n"; while(again()); } how do you code a looping construct so that it continues if a boolean function returnsfalse rather than true?

5. Program Stack • program (call) stack – means of RAM allocation for local function variables. • last-in/first-out (LIFO) data structure • function frame unit of allocation • contains local variables, parameters, return value void a(void); void b(void); void c(void); int main(void){ a(); } void a(void){ b(); c(); } void b(void){ ; // does not do anything }   void c(void){ ; // does not do anything }

6. Call-by-Reference • what was call-by-value? • call-by-reference is a parameter passing discipline that allows the function to modify the arguments • to distinguish call-by-reference, an ampersand (&) precedes the parameter declaration both in the function head and in the function prototype • the function call is not distinguishable (careful!) • prototype void get_intput(double &fard); // extended form void get_intput(double &); // abbreviated form • definition void get_intput(double &fard){ cout << “I will convert Fahrenheit Temperature ” << “to Celsius.\n” << “Enter temperature in Fahrenheit: “; << “ degrees Celsius.\n”; cin >> fard; } • mixing call kinds of parameters is allowed: myfunc(int&,double,int&);

7. Call-by-Reference (Cont.) • function invocations for call-by-reference and call-by-value are similar but not the same: double f_temp; get_input(f_temp); • passing expressions by reference is not allowed! get_input(23.0); // WRONG! • in call-by-reference the function operates on the memory location of the argument • functions that need to return more than one value usually use call-by-reference: prototype: void get_numbers(int& input1, int& input2); call: get_numbers(first_num, second_num); • passing one similar value as return and the other as parameter is bad style: prototype: int get_numbers(int& input2); // BAD call: first_num=get_numbers(second_num); // STYLE

8. Call-by-Reference, Example • this function swaps the values of arguments void swapValues(int& var1, int& var2){ int temp; temp = var1; var1 = var2; var2 = temp; } • what is output when this code is executed? int i=1, j=2; swapValues(i,j); cout << i << ’ ’ << j;