Monday, Jan 13, 2003Kate Gregory with material from Deitel and Deitel Week 2 Questions from Last...

Monday, Jan 13, 2003 Kate Gregorywith material from Deitel and Deitel

Week 2

• Questions from Last Week

• Control Structures

• Functions

• Lab 1


Course ScheduleDate Week Topic Chapter Hand Out Due Back Test

6-Jan-03 1Administrivia / Overview / Intro to C++ / Control Structures 1

13-Jan-03 2Functions / Arrays, Pointers, Strings 2,3,4,5 Lab 1 / Lab 2

20-Jan-03 3 Classes, Data Abstraction 6 Lab 1 5%27-Jan-03 4 More on Classes 7 Lab 3 Lab 2 5%3-Feb-03 5 No Lecture

10-Feb-03 6 Operator Overloading 8 Lab 4 Lab 3 5%17-Feb-03 Reading Break24-Feb-03 7 Inheritance 9 Lab 4 5% Midterm 25%

3-Mar-03 8Virtual Functions and Polymorphism 10 Lab 5

10-Mar-03 9 Stream IO 11 Lab 6 Lab 5 5%17-Mar-03 10 Templates 12,13 Lab 7 Lab 6 5%24-Mar-03 11 Exceptions31-Mar-03 12 File IO 14 Lab 7 5%

??? Exam Final 40%


Control Structures

• Normally execution falls from one statement to another:

i++;

j++;

x = y;


Conditions

• if

• else

• switch

• Immediate if / ternary operator


Repetitions

• while

• for

• do / while


if

if ( x > 0) y = 2;z = 3;

if ( x > 0){ y = 2; z = 3;}


If Gotchas

• Round brackets around the condition are never optional

• The condition can be true or false, or a number. • All non-zero numbers are true. Only zero is false.• Never put a ; after the round brackets

if ( x > 0);

y = 2;


Comparison Operators

• Greater Than >

• Greater Than or Equal To >=

• Less Than <

• Less Than or Equal To <=

• Equal To ==

• Not Equal To !=


Two conditions

if ( x > 0)

if (y < 0)

cout << "lower right";• Alternatively:

if ( x > 0 && y < 0)

cout << "lower right";


Logical Operators• && ( logical AND )

– Returns true if both conditions are true• || ( logical OR )

– Returns true if either of its conditions are true• ! ( logical NOT, logical negation )

– Reverses the truth/falsity of its condition– Unary operator, has one operand

• Useful as conditions in loopsExpression Resulttrue && false falsetrue || false true!false true


Expressions in Conditions

if (x+3 > y)

if (sin(x) > 0)

if (sin(x) > 0 && foo(y) < 0 )– Short-circuiting


Else

if ( x > 0)

y = 2;

z = 3;

if ( x > 0)

y = 2;

else

z = 3;


Switch

if (x == 1)

cout << “one”;

else

if ( x == 2)

cout << “two”;

else

if ( x == 3)

cout << “three”;


Switch

switch (x){case 1: cout << “one”; break;case 2: cout << “two”; break;case 3: cout << “three”; break;default: cout << “not 1, 2, or 3”;}


Switch errors

• Forgetting the {}

• Forgetting the break statements

• Forgetting a default case


Immediate if

• Also called ternary operator

x = y>0? 3 : 6;

Equivalent to

if (y>0)

x=3;

else

x=6;


while

x = 0;

while (x < 10)

{

cout << x << ‘\n’ ;

x ++;

}


for

for (x = 0; x < 10; x ++)

{

cout << x << ‘\n’ ;

}

• Eliminates forgetting to increment

• Remember to use ; not ,


While over for

• If you know how many times, use for

• If you don’t, use while– While not at the end of the file– While the user still wants to continue


Do

x = 11;

do

{

cout << x << ‘\n’ ;

x ++;

} while (x < 10)


Break

• Used for exiting a loop immediatelyx = 0;

while (x < 10)

{

if ( x > 4)

break;

cout << x << ‘\n’ ;

x ++;

}


Continue

• Used for skipping the remainder of the body of a loop

x = 0;while (x < 10){ if ( x > 4) continue; cout << x << ‘\n’ ; x ++;}


Continue in for

for (x = 0; x < 10; x ++){ if ( x > 4) continue; cout << x << ‘\n’ ;}

• Continue in a while is only safe after you’ve incremented or moved to the next


Functions and Methods

• Really two words for the same thing.

• A function that is part of a class is called a member function. OO purists sometimes call it a method.

• A function that is not part of a class is called a global function.– The main() function is a global function


Global functions

• Gather up some code to make a single thing

• Perhaps because it’s used in many places

• Perhaps because you can understand your code better if it’s not a 10,000 line monolith

• Perhaps to simplify team programming

• Library code may be available as functions


Declare a function

int foo (int x, int y);

void bar(float f);

void report(void);

void deleteFiles();• Also called prototyping a function

• Placeholder names are optional, but always use them


Where to declare

• All code that calls the function must declare it first, so the compiler knows about it

• If the declaration is missing the compiler will complain

• Often a number of declarations are gathered into a header file


Implement a function

void report(void){ cout << “This is a report”; return;}• For void functions you can omit the return• Only have the implementation in one file• If it’s missing the linker will complain• Also called defining a function


Call a function

int i;

i = foo ( 3, 4);• OK to ignore return values

foo (5,6);• Compiler will check types

i = foo(“Hello”, 4.5);


Call By Value

void ChangeIt (int a)

{

a++ ;

}• Some code calls it

int i=3;

ChangeIt(i);


Call By Reference

void ChangeIt (int& a)

{

a++ ;

}• Some code calls it

int i=3;

ChangeIt(i);


Reference Advantages

• When passing objects, the copy can be quite expensive

• You might want the function to change its parameters

• The C way, with pointers, makes code hard to read


Simple function example

int DoubleIt(int a){ return 2 * a;}int main(){ int x; cout << “Enter a number ”; cin >> x; cout << “Double that is “ << DoubleIt(x); return 0;}


Scope

• Variables come into scope when they are declared• They go out of scope when they hit a brace

bracket:{int i = 3;

}i = 7; //compiler error

• Generally this is an issue when you declare something inside the block of an if/for/while and then try to use it afterwards


For Next class

• Complete Lab 1– Late penalty is TERRIBLE

• Read chapters 4 and 5

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Monday, Jan 13, 2003Kate Gregory with material from Deitel and Deitel Week 2 Questions from Last...

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