C++ L05-Functions

Mohammad Shaker
mohammadshaker.com
@ZGTRShaker
2010, 11, 12, 13, 14
C++
Programming Language
L04-FUNCTIONS

Functions
•Why function?
•functions procedures in c++
•What’s the function prototype (declaration) definition?
•Function signature (2010 exam Question)
–What’s it?
–It’s just the name of the function with its parameters
•No return type!!!! (Return type is not considered as part of the function’s signature!, guess why?)
intfoo(int);// function prototype
foo(int) // function signature

Functions
#include<iostream>
usingnamespace::std;
intfoo(int);// function prototype
intmain()
{
return0;
}
#include<iostream>
foo(int); // function prototype
intmain()
{
return0;
}
Compiler error, missing return type

Functions
•The following are the same
#include<iostream>
intMult( intx ) // note there's no; when we
// write the definition here
{
x = x * 2;
returnx;
}
void main()
{
}
#include<iostream>
intMult( intx );
void main()
{}
intMult( intx )
{
x = x * 2;
returnx;
}

Functions
•The following are the same
#include<iostream>
intMult( int x )
{
x = x * 2;
returnx;
}
void main()
{
}
#include<iostream>
intMult(int); // we didn’t write the x
// pirmeted when prototype only
void main()
{}
intMult( intx )
{
x = x * 2;
returnx;
}

Functions
#include<iostream>
intMult(int);
void main()
{
Mult (3);
}
intMult( intx )
{
x = x * 2;
returnx;
}
#include<iostream>
intMult(int);
void main()
{
cout << Mult(3);
}
intMult( intx )
{
x = x * 2;
returnx;
}
6

Functions
#include<iostream>
intMult(int);
void main()
{
Mult(3);
}
intMult( intx )
{
x = x * 2;
cout << x;
return0;
}
#include<iostream>
intMult(int);
void main()
{
int c = 3;
Mult(c);
}
intMult( intx )
{
x = x * 2;
cout << x;
return0;
}
6
6

Functions
#include<iostream>
intMult(int);
void main()
{
int x = 3;
Mult(x);
}
intMult( intx )
{
x = x * 2;
cout << x;
return0;
}
#include<iostream>
intMult(int);
void main()
{
int x = 3;
Mult(x);
cout << x;
}
intMult( intx )
{
x = x * 2;
cout << x;
return0;
}
6
6

Functions
#include<iostream>
intMult(int);
void main()
{
int x = 3;
Mult(x);
cout << endl;
cout << x;
}
intMult( intx )
{
x = x * 2;
cout << x;
return0;
}
#include<iostream>
intMult(int);
void main()
{
int x = 3;
Mult(x);
cout << x;
}
intMult( intx )
{
x = x * 2;
cout << x << endl;
return0;
}
6
3
6
3

Functions
#include<iostream>
intMult(int);
void main()
{
int x = 3;
cout << Mult(x) << endl;
cout << x;
}
intMult( intx )
{
x = x * 2;
returnx;
}
#include<iostream>
void Mult(void);
void main()
{
int x = 3;
Mult() << endl;
cout << x;
}
voidMult( void )
{
int x = 3;
cout << x * 2 << endl;
}
6
3
Compiler error

Functions
#include<iostream>
void Mult(void);
void main()
{
int c = 3;
Mult() << endl;
cout << c;
}
voidMult( void )
{
int x = 3;
cout << x * 2 << endl;
}
#include<iostream>
void Mult(void);
void main()
{
Mult() << endl;
}
voidMult( void )
{
int x = 3;
x = x * 2;
return0;
}
Compiler error
Compiler error, return 0; with void function

Functions
#include<iostream>
void Mult(void);
void main()
{
cout << Mult() << endl;
}
voidMult()
{
int x = 3;
x = x * 2;
}
#include<iostream>
void Mult(void);
void main(void)
{
Mult();
}
voidMult(void)
{
int x = 3;
x = x * 2;
}
Compiler error, cout with void return funtion
At last everything’s working

Functions
#include<iostream>
void Mult(void);
void main(void)
{
Mult();
}
voidMult(void)
{
int x = 3;
x = x * 2;
}
#include<iostream>
void Mult();
void main()
{
Mult();
}
voidMult()
{
int x = 3;
x = x * 2;
}
Compile and run
Compile and run. In the parameter list, voidor empty is the same

Functions
#include<iostream>
voidMult(void);
voidmain()
{
Mult();
}
Mult()
{
int x = 3;
x = x * 2;
}
#include<iostream>
Mult(void);
voidmain()
{
Mult();
}
void Mult()
{
int x = 3;
x = x * 2;
}

Functions
#include<iostream>
void Mult(void);
void main(void)
{
Mult();
}
int Mult(void)
{
int x = 3;
x = x * 2;
returnx;
}
#include<iostream>
int Mult(void);
void main(void)
{
Mult();
}
void Mult(void)
{
int x = 3;
x = x * 2;
}
Compiler error, return type differs
Compiler error, return type differs

Functions
#include<iostream>
int Mult(void);
void main(void)
{
}
int Mult(void)
{
int x = 3;
x = x * 2;
returnx;
}
#include<iostream>
int Mult(void);
void main(void)
{
}
int Mult(void)
{
int x = 3;
returnx * 2;
}
6
6

Functions
#include<iostream>
int Mult(void);
void main(void)
{
}
int Mult(void)
{
int x = 3;
returnx * 2; cout << x << end;
}
#include<iostream>
int Mult(int x);
void main(void)
{
}
int Mult(int x)
{
returnx * 2;
}
6
Compiler error, no variable passed to function
Nothing got excuted after the return statement

Functions
#include<iostream>
int Mult(int x);
void main(void)
{
cout << Mult(3) << endl;
}
int Mult(int x)
{
returnx * 2;
}
#include<iostream>
int Mult(int x);
void main(void)
{
cout << Mult(3) << endl;
}
int Mult(int x)
{
intx = 2;
returnx * 2;
}
0
Compiler error, redefinition of variable x

Functions
#include<iostream>
intMult(int, int);
voidmain(void)
{
inti1, i2;
cout << Mult(i1,i2) << endl;
}
intMult(intx, inty)
{
returnx * 2;
}
#include<iostream>
intMult(int, int);
voidmain(void)
{
inti1, i2;
}
intMult(intx, y)
{
returnx * 2;
}
6
Compiler error, missing type for y

Functions
#include<iostream>
intMult(int, int);
voidmain(void)
{
inti1, i2;
}
intMult(intx, inty)
{
if(x = 2 )
{
return3;
}
else
{
returnx * 2;
}
}
#include<iostream>
intMult(int, int);
voidmain(void)
{
inti1, i2;
}
intMult(intx, inty)
{
int MeMe (int z)
{
return 0;
}
}
3
Compiler error, can’t define a function inside another one

Functions
#include<iostream>
intMult(int, int);
voidmain(void)
{
floati1= 3.4, i2;
}
intMult(intx, inty)
{
return2*x;
}
#include<iostream>
intMult(int);
voidmain(void)
{
for(inti = 0; i<=10; i++)
{
cout << Mult(i) << "-";
}
cout << “hehe” << endl;
cout<< endl;
}
intMult(intx )
{
return2*x;
}
6
0-2-4-6-8-10-12-14-16-18-20-hehe
Press any key to continue

Functions
#include<iostream>
voidCrazy1();
voidCrazy2(int);
voidmain(void)
{Crazy1(); }
voidCrazy1()
{
intx = 3;
Crazy2(x);
cout << x;
}
voidCrazy2(intx )
{
x+=6;
cout << x << endl;
}
9
3

Headers
•The Concept of headers

Headers File
•What’s a header?
–Moving functions out side the main program
•Logical groups
–Stored in their own files
•How to do it?
–By Moving
•function declarations
–Into headers files
»(.h) files // header files
•function definitions
–Into source files
»(.cpp) files // source files
–Note: function definitions can’t be split up into multiple files!

cmathand sqrt
#include<iostream>
#include<cmath>
voidmain(void)
{
cout << sqrt(100.0) << endl;
}
#include<iostream>
voidmain(void)
{
cout << sqrt(100.0) << endl;
}
10
Compiler error identifier not found
•To use it
–Include <cmath>

cmathand sqrt
#include<iostream>
#include<cmath>
voidmain(void)
{
cout << sqrt(100) << endl;
}
#include<iostream>
#include<cmath>
voidmain(void)
{
cout << sqrt(sqrt(100.0)) << endl;
}
Compiler error, can’t use integer “no overloaded function”
3.16228

cmathand sqrt
#include<iostream>
#include<cmath>
voidmain(void)
{
intx;
cout << sqrt(6*x) << endl;
}
#include<iostream>
#include<cmath>
voidmain(void)
{
doublex = 3;
}
Compiler error, can’t use integer “no overloaded function”
3

cmathand sqrt
#include<iostream>
#include<cmath>
voidmain(void)
{
float x = 3;
}
3

rand()
•Random number
–rand()
–Needs to include <cstdlib>
•Generates unsigned integers
–Between
»0 (Zero :D)
»Rand_Maxnumber (usually 32767)

rand()
#include<iostream>
#include <cstdlib>
voidmain(void)
{
intx = 3;
x = rand();
cout << x << endl;
}
41
Now, when compiling many times
Every time we have the same random value!
41
41
41

rand()
#include<iostream>
voidmain(void)
{
intx = 3;
x = rand();
cout << x << endl;
}
#include<iostream>
#include <cstdlib>
voidmain(void)
{
intx = 3;
x = rand();
cout << x << endl;
cout << x << endl;
}
54
156
156
Works without <cstlib>

rand()
#include<iostream>
#include <cstdlib>
voidmain(void)
{
intx = 3;
x = rand();
cout << x << endl;
x = rand();
cout << x << endl;
}
156
12356

srand()
•srand()
–#include <cstdlib>
–Give a starting value for the rand()function
–Usually used once in program

srand()
#include<iostream>
#include<ctime>
voidmain(void)
{
intx = 3;
srand (time(0));
cout << x << endl;
}
#include<iostream>
#include<ctime>
voidmain(void)
{
intx = 3;
srand (time());
cout << x << endl;
}
3
Compiler error, need value for time()

What happened when compiling many times?
srand()
#include<iostream>
#include<ctime>
voidmain(void)
{
intx = 3;
srand (time(0));
x = rand ();
cout << x << endl;
}
456
Now, when compiling many times. Every time we have a new differentvalue
12345
189
What happened when compiling many times?
#include<iostream>
#include<ctime>
voidmain(void)
{
intx = 3;
srand (5);
x = rand ();
cout << x << endl;
}
48
Not an appropriate srand() paramater leads to insufficient using of srand()!!!
48
48

srand() with clock()
#include<iostream>
#include<ctime>
voidmain(void)
{
srand(clock());
// clock is from <ctime>
// no needs to value for clock ()
for(inti = 0; i < 10; i++)
cout << rand() << endl;
}
714
4415
16337
2807
14052
5430
30050
16163
20477
3146

rand()
•Scaling & shifting
–%
•x % y // returns a value between 0 to y-1
•let’s see an example
#include<iostream>
#include<cstdlib>
voidmain(void)
{
inti;
i = rand() % 6 + 1;
// rand() % 6: number between 0 to 5
// +1: makes a shift of the range we have
// 0 to 5 becomes 1 to 6
cout << i << endl;
// here will print a number absolutely between 1 to 6
}
6
Or any other number between 1 and 6

Variables and Storage
•Name, type, size, values
•Storage class
–Period variable living in memory
•Linkage
–Multiple-file processing, which files can use it.
•Scope
–Variable can be referenced in program

Storage Classes
autokeyword
Can used Explicitly
auto double x;
registerkeyword
High speed register
register double x = 4;
statickeyword (Very important)
function’s local variables
Keeps values between functions call
Known ONLY in ITS OWN function
Static double x = 3;
extern key word
Global variables accessible to functions in Same file, Other files
Must be declared in each file which has been used in.
Used to access Global variable in another file

Storage Classes
#include<iostream>
voidmain(void)
{
auto register double x = 4;
}
#include<iostream>
voidmain(void)
{
register auto double x = 4;
}
Compiler error, can’t use both at the same time
Compiler error, can’t use both at the same time
#include<iostream>
voidmain(void)
{
auto double x = 4;
}
#include<iostream>
voidmain(void)
{
register double x = 4;
}
Compile and run
Compile and run

StaticStorage (Very important)
#include <iostream>
using namespace std;
void StaticMyHeadache()
{
static intx = 8;
cout<< "In function, x = " << x << endl;
x*=2;
cout<< "In function, x = " << x << endl;
}
intmain()
{
intx = 3;
cout<< x << endl;
StaticMyHeadache();
cout<< x << endl;
StaticMyHeadache();
}
Defined and initialized at the same time in the first time of calling the function then the compiler no longer parse this line of code
3
In function, x = 8
In function, x = 16
3
In function, x = 16
In function, x = 32

extern Storage
•1stfile
•2ndfile
#include<iostream>
voidmain(void)
{
intMyGlobalVar;
}
#include<iostream>
extern intMyGlobalVar;

extern Storage
•1st file
•2ndfile
#include<iostream>
voidmain(void)
{
intMyGlobalVar;
}
#include<iostream>
voidmain(void)
{
extern intMyGlobalVar;
}
Compiler error, why?
2 “main”s in the same project! that’s wrong! Any project in the world will only have one main

InlineFor small, common-used functionsNo function call, just copy the code into the programCompiler can ignore Inline

Inline functions
#include<iostream>
intMultiplyByFive(int);
voidmain( )
{
intx;
cout << "Enter a number: ";
cin>>x;
cout<<"n The Output is: "<< MultiplyByFive(x) << endl;
}
inlineintMultiplyByFive (intx1)
{
return5*x1;
}
Enter a number: 2
The Output is: 10

Blocks and Scopes
•Scopes
–Local Scopes
–Global Scopes
•The Golden Rule
–Life time of block scope variables is lifetime of block
–Variables are stored in a memory stack

Variables are stored in a stack

Variables are stored in a stack
That means, first in Last OUT and VICE VERSA!

Blocks and Scopes
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
cout << "This is inner block "<< endl;
}
}
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
cout << x << endl;
}
}
This is inner block
9

Blocks and Scopes
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
cout << x << endl;
}
cout << x << endl;
}
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
intx = 4;
cout << x << endl;
}
}
9
9
4

Blocks and Scopes
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
intx;
x = 4;
cout << x << endl;
}
cout << x << endl;
}
#include<iostream>
voidmain(void)
{
intx = 9, y = 3;
{
intx = 4;
cout << x << endl;
}
cout << y << endl;
}
4
9
4
3

Blocks and Scopes
#include<iostream>
voidmain(void)
{
intx = 9;
{
intx = 4, y = 3;
cout << x << endl;
}
cout << y << endl;
}
Compiler error, y undeclared identifier

Blocks and Scopes
#include<iostream>
intx = 35;// Global Variable
voidbar()
{
intx = 3;// local Variable
}
voidmain(void)
{
intx = 9, y = 3;
{
}
cout << x << endl;
}
#include<iostream>
intx = 35;//Global Variable
voidbar()
{
}
voidmain(void)
{
intx = 9, y = 3;
{
}
cout <<::x << endl;
}
9
35

Blocks and Scopes
#include<iostream>
voidbar()
{
cout <<::x << endl;
}
voidmain(void)
{
intx = 9, y = 3;
{
}
}
#include<iostream>
voidbar()
{
cout << x << endl;
}
voidmain(void)
{
intx = 9, y = 3;
{
}
bar();
}
Compile & Run
3

Blocks and Scopes
#include<iostream>
voidbar()
{
cout << ++::x << endl;
}
voidmain(void)
{
intx = 9, y = 3;
{
}
bar();
}
#include<iostream>
voidbar()
{
cout <<::x++ << endl;
}
voidmain(void)
{
intx = 9, y = 3;
{
}
bar();
cout <<::x << endl;
}
35
34
35

Quiz -1
#include<iostream>
intx = 34;
voidfoo()
{
staticintx = 3;// initialized only ONE time
cout << "first x in foo = "<< x << endl;
x++;
cout << "second x in foo = "<< x << endl;
}
voidmain(void)
{
intx = 9;
cout << x << endl;
{
intx = 5;
cout << x << endl;
}
cout << x << endl;
foo();
foo();
cout << x << endl;
cout <<::x << endl;
}
9
5
9
first x in foo = 3
second x in foo = 4
first x in foo = 4
second x in foo = 5
9
34

Quiz -2
#include <iostream>
using namespace::std;
intx = 34;
void foo()
{
static intx = 3;// initialized only ONE time
x = 5;
cout<< "first x in foo = " << x << endl;
x++;
cout<< "second x in foo = " << x << endl;
}
voidmain(void)
{
intx = 9;
cout << x << endl;
{
intx = 5;
cout << x << endl;
}
cout << x << endl;
foo();
foo();
cout << x << endl;
cout <<::x << endl;
}
9
5
9
first x in foo = 5
second x in foo = 6
first x in foo = 5
second x in foo = 6
9
34

Quiz –3, 4
#include<iostream>
intx = 34;
voidfoo()
{
static intx = 3;
intx = 3;
x++;
}
Does this function runs?
Compiler error, redefinition of x
#include<iostream>
intx = 34;
voidfoo()
{
staticx = 3;
x = 5;
x++;
}
Does this function runs?
Compiler error, missing type after static

Default Parameters
#include<iostream>
voidprint(intx=0, intn=4 )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3);
}
2
#include<iostream>
ints = 0;
voidprint(intx=0, intn )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3);
}
Compiler error, missing default value for parameter 2
When defaultinga parameter,all other parameters -if exist -on the right sideshould be defaulted too

Default Parameters
#include<iostream>
voidprint(intx, intn=0 )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3);
}
2
#include<iostream>
voidprint(intx, intn, inty )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3,4);
}
2

Default Parameters
#include<iostream>
ints = 0;
voidprint(intx, intn, inty = 0 )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3,4);
}
2
#include<iostream>
ints = 0;
voidprint(intx, intn, inty = 0 )
{
cout << x << endl;
}
voidmain(void)
{
print(2,3);
}
2

Default Parameters
#include<iostream>
ints = 0;
voidprint (intx, intn, inty=10 )
{
cout << x << endl;
cout << n << endl;
cout << y << endl;
}
voidmain(void)
{
print(2,3);
}
2
3
10

Default Parameters
#include<iostream>
ints = 0;
voidprint(intx, intn=10, inty )
{
cout << x << endl;
cout << n << endl;
cout << y << endl;
}
voidmain(void)
{
print(2,3);
}
Compiler error. y is not defaulted.

Default Parameters
#include<iostream>
ints = 0;
{
cout << x << endl;
cout << n << endl;
cout << y << endl;
}
voidmain(void)
{
print(2,3);
}
The compiler doesn’t know what to do?
Should it replace the value (3) with the default value of the defaulted parameter (n) or go on to the next parameter (y) and pass it through

Default Parameters
#include<iostream>
ints = 0;
{
cout << x << endl;
cout << n << endl;
cout << y << endl;
}
voidmain(void)
{
print(2,3);
}
And nowyou can know whythe compiler can parse the function calling correctly when the function header have the defaulted parameter at the right most of the prototype and not in the middle
coz as you saw, the compiler couldn’t determine where to pass the value!
The compiler doesn’t know what to do?
Should it replace the value (3) with the default value of the defaulted parameter (n) or go on to the next parameter (y) and pass it through

Default Parameters
#include<iostream>
ints = 0;
voidprint(intx, intn=10, inty = 5 )
{
cout << x << endl;
cout << n << endl;
cout << y << endl;
}
voidmain(void)
{
print(2,3);
}
2
3
5

Calling by valueVS calling by reference

Calling by value VS calling by reference
•Calling by value
–Copy of data
–Changes to copy don’t affect original
–Prevent an unwanted side effect
•Calling by reference (&)
–Function directly access data
–Changes affect original (no copy exist here!)
–Using & after data type
•void foo(double & x)

#include<iostream>
ints = 0;
voidFuncByValue (intx )
{
cout << "In function before multiplication, x = "<< x << endl;
x = x*4;
cout << "In function after multiplication, x = "<< x << endl;
}
voidmain(void)
{
intx = 2;
cout << "In main, before calling the function "<< x << endl;
FuncByValue(x);
cout << "In main, after calling the function "<< x << endl;
}
In main, before calling the function 2
In function before multiplication, x = 2
In function after multiplication, x = 8
In main, after calling the function 2
#include<iostream>
ints = 0;
voidFuncByRef (int& x )
{
x = x*4;
}
voidmain(void)
{
intx = 2;
FuncByRef (x);
}
In main, before calling the function 2
In main, after calling the function 8

#include<iostream>
ints = 0;
voidFuncByRef (& intx )
{
x = x*4;
}
voidmain(void)
{
intx = 2;
FuncByRef (x);
}
Compiler error, & before type
#include<iostream>
ints = 0;
voidFuncByRef ( intx & )
{
x = x*4;
}
voidmain(void)
{
intx = 2;
FuncByRef (x);
}
Compiler error, & after variable

#include<iostream>
ints = 0;
intFuncByValue ( intx )
{
x = x*4;
returnx;
}
voidmain(void)
{
intx = 2;
cout << "In main, before calling the function, x = "<< x << endl;
cout << FuncByValue(x) << endl;
cout << "In main, after calling the function, x = "<< x << endl;
}
In main, before calling the function, x = 2
8
In main, after calling the function, x = 2
#include<iostream>
ints = 0;
intFuncByRef ( int& x )
{
x = x*4;
returnx;
}
voidmain(void)
{
intx = 2;
cout << "In main, before calling the function, x = "<< x << endl;
cout << FuncByRef(x) << endl;
cout << "In main, after calling the function, x = "<< x << endl;
}
In main, before calling the function, x = 2
8
In main, after calling the function, x = 8

Function Overloading
•Is a function with
–same name
–different parameters
–(Not the return type!)
•That means that the overloaded functions are distinguished in Signature
–(Not the return type!)

#include<iostream>
ints = 0;
intf ( int&x )
{
x = x * 2;
returnx;
}
intf ( float&x )
{
x = x * 3;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
cout << f(y1) << endl;
}
4
6
Oveloading but with warning (casting)
#include<iostream>
ints = 0;
intf ( int&x )
{
x = x * 2;
returnx;
}
float f ( float&x )
{
x = x * 3;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
}
4
6
No warnings

#include<iostream>
ints = 0;
intf ( intx )
{
x = x * 2;
returnx;
}
float f ( floatx )
{
x = x * 3;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
}
4
6
#include<iostream>
ints = 0;
intf ( intx )
{
x = x * 2;
returnx;
}
float f ( floatx )
{
x = x * 0;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
}
4
0

#include<iostream>
ints = 0;
intf ( intx, intz)
{
x = x * 2;
cout << x << endl;
cout << z << endl;
returnx;
}
floatf (floatx, intz)
{
x = x * 3;
cout << x << endl;
cout << z << endl;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
intz1 = 3, z2 = 2;
f(y1,z1);
f(y2,z2);
}
4
3
6
2
No warnings
#include<iostream>
ints = 0;
intf ( intx, intz)
{
x = x * 2;
cout << x << endl;
cout << z << endl;
returnx;
}
floatf (floatx, intz)
{
x = x * 3;
cout << x << endl;
cout << z << endl;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
float z1 = 3, z2 = 2;
f(y1,z1);
f(y2,z2);
}
4
3
6
2
Warnings

#include<iostream>
ints = 0;
intf ( intx, intz)
{
x = x * 2;
cout << x << endl;
cout << z << endl;
returnx;
}
floatf (intz, floatx)
{
x = x * 3;
cout << x << endl;
cout << z << endl;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
intz1 = 3, z2 = 2;
f(y1,z1);
f(y2,z2);
}
4
3
4
2
Warnings
#include<iostream>
ints = 0;
intf ( intx, intz)
{
x = x * 2;
cout << x << endl;
cout << z << endl;
returnx;
}
floatf (intz, floatx)
{
x = x * 3;
cout << x << endl;
cout << z << endl;
returnx;
}
voidmain(void)
{
inty1 = 2;
floaty2 = 2;
float z1 = 3, z2 = 2;
f(y1,z1);
f(y2,z2);
}
9
2
6
2
Warnings

#include<iostream>
intx = 0;
floatf2 (intz )
{
cout << z << endl;
z*=2;
returnz;
}
voidf1 ( int&x )
{
x+2;
cout << x << endl;
f2(x);
cout << x << endl;
}
voidmain(void)
{
f1(::x++);
cout << ++::x << endl;
}
Compiler error Can’t convert from int to &int
#include<iostream>
intx = 0;
voidf1 ( int&x )
{
x+2;
cout << x << endl;
f2(x);
cout << x << endl;
}
floatf2 (intz )
{
cout << z << endl;
z*=2;
returnz;
}
voidmain(void)
{
f1(::x);
cout <<::x << endl;
}
Compiler error. f1 can’t know what f2 is!

Quiz 1
voidmain(void)
{
intx = 9;
cout << x << endl;
{
{
intx = 5;
cout << x++ << endl;
}
cout << x << endl;
::x = x+2;
}
cout << x << endl;
{
foo();
foo();}
cout << x << endl;
cout <<::x << endl;
}
9
5
9
9
first x in foo = 5
second x in foo = 6
first x in foo = 5
second x in foo = 6
9
11
#include <iostream>
using namespace::std;
intx = 34;
void foo()
{
static intx = 3;// initialized only ONE time
x = 5;
cout<< "first x in foo = " << x << endl;
x++;
cout<< "second x in foo = " << x << endl;
}

Quiz 2
#include<iostream>
voidTryMe();
voidmain()
{
cout<<"In main"<<endl;
TryMe();
}
voidTryMe()
{
cout<<"In function"<<endl;
main();
}
In main
In function
In main
In function
In main
In function
In main
In function
In main
In function

Quiz 3
#include<iostream>
voidTryMe()
{
cout<<"In function"<<endl;
main();
}
voidmain()
{
TryMe();
cout<<"In main"<<endl;
}
Compiler error!
TryMe() can’t know what a main function is

C++ L05-Functions

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