Multiple Files Revisited
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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”
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why are programs included in multiple files
what are object files and how are they related to multiple file-program
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what is linking?
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1
Programmer-Defined Functions II
Void Functions, Boolean Functions
Program Stack, Call-by-Reference
Void Functions
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void function – does not return a value, can be used only as a standalone
statement
void is specified as return type
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return-statement is not necessary; if used, cannot contain expression
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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
}
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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(){
cout << "Again: [y/n] ";
char answer;
cin >> answer;
if (answer == 'y')
int main(){
return true;
do
else
cout << "Hello, World!\n";
while(again());
return false;
}
}
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how do you code looping construct so that it continues if boolean function returns
false rather than true?
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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 b(){
void a();
; // does not do anything
void b();
}
void c();
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int main(){
a();
}
void c(){
; // does not do anything
}
void a(){
b();
c();
}
5
Call-by-Reference
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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 ampersand (&) precedes parameter declaration
both in function head and in function prototype
 function call is not distinguishable
prototype
void getIntput(double &fard); // extended form
void getIntput(double &); // abbreviated form
definition
void getIntput(double &fard){
cout << ”I will convert Fahrenheit Temperature ”
<< ”to Celsius.\n”
<< ”Enter temperature in Fahrenheit: ”;
<< ” degrees Celsius.\n”;
cin >> fard;
}
mixing calls of parameters is allowed: myfunc(int&, double, int&);
6
Call-by-Reference (Cont.)
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function invocations for call-by-reference and call-by-value are similar but not the
same:
double temp;
getInput(temp);
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passing expressions by reference is not allowed!
getInput(23.0); // WRONG!
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in call-by-reference the function operates on the memory location of the
argument
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functions that need to return more than one value usually use call-by-reference:
prototype: void getNumbers(int& input1, int& input2);
call: getNumbers(one, two);
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passing one similar value as return and the other as parameter is bad style:
prototype: int getNumbers(int& input2); // BAD
call: one=getNumbers(two);
// STYLE
7
Call-by-Reference, Example
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this function swaps the values of arguments
void swapValues(int& left, int& right){
int temp;
temp = left;
left = right;
right = temp;
}
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what is output when this code is executed?
int i=1, j=2;
swapValues(i,j);
cout << i << ’ ’ << j;
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