Output can be to a screen, to files, to other output

devices, to other programs, and to other parts of a program. Examples of output

devices include network interfaces, music synthesizers, electric motors, light generators,

heaters, etc.

Inputs to a part of a program. 

outputs from a program part. 

Hide details that we don't need to usc a facility ("implementation details") behind a convenient and general interface. we access it through typed and named

variables

taking a large problem and dividing it into several

little ones.

The most basic building block of programs is an expression. An expression computes

a value from a number of operands. The simplest expression is simply a literal value, such as 10, 'a', 3.14, or "Norah". Names and variables are also expressions.

Are the following expressions?

int length = 20;

int width = 40;

int area = length*width

What does this mean?

length = 99;

99 is the value found in the variable length. 99 has initialized the variable. Here, length means "the object

named length," so that the assignment expression is read "Put 99 into the object named by length." We distinguish between length used on the left-hand side of an assignment or an initialization (" the lvalue of length" or "the object named by length") and length used on the right-hand side of an assignment or initialization

(" the rvalue of length," "the value of the object named by length," or just "the value of length")

Which code is correct in determining perimeter?

1. int perimeter = length*2+width*2

2. int perimeter = length+width*2

3. int perimeter = (length+width)*2

The usual mathematical rules of operator precedence apply, so length+ width*2 means le ngth+(width*2). Similarly a* b+c/d means (a* b)+(cld) and not

a*( b+c)/d.

ugly code slows down reading and comprehension.

Ugly code is not often just hard to read, it is also much harder to get correct. Ugly code often hides logical errors.

a symbolic constant, that is, a named object to which you can't give a new value after it has been initialized. For example:

const double pi = 3.14159

You cannot reassign pi. for instance, saying pi=7 would just cause the compiler to read const pi. 

Define a constant expression

expression with an integer value composed exclusively of constants. For example:

const int max=17; //a literal is a constant expression

int val=9

max+2 //a constant expression (const plus a literal)

val+2 //not a const expression.

Name these operators:

f(a)

++ival

--ival

!a

-a

a*b

a/b

a%b

Function call

pre increment

pre decrement

not

unary minus

multiply

divide

modulo

Name these operators:

a+b

a-b

out<<b

in>>b

a<b

a<=b

a>b

a>=b

add 

subtract

white b to out

read in into b

less than

less than or equal

greater than

greater than or equal

Name these operators:

a==b

a!=b

a && b

a || b

ival = a

ival *=a

equal

not equal

logical and

logical or

assignment

compound assignment 

a<b<c means (a<b)<c and that a<b evaluates to a Boolean value: True or false. So, a<b<c will be equivalent to either True<c or false<c. In particular,

a<b<c docs not mean "Is b between a and c?".

What are the three ways an increment can be expressed?

What is the most preferred method for expression incrementation? Why?

++a

a+=1

a=a+1

Method one is the most preferred because it expresses what we want to do most logically, and leaves no room for guessing whether we meant to increment by 1 or just made an error. 

What is wrong with this code?

double dc;

cin>>dc;

double df=9/5*dc+32;

What does the compiler do to statements that follow one another? 

example:

 int a =7;

cout << a << '\n';

generally looks like  

if {x == 5};

{ y = 3;}

These statements do nothing, even though they're legal constructs in C++. The compiler will not alert you to these errors. 

What happens in this empty statement? 

if {x == 5};

{ y = 3;}

The compiler will test x to see if it has

the value 5. If this condition is true, the following  statement (the empty statement) will be executed, with no effect. Then the program continues to the next

line, assigning the value J to y (which is what you wanted to have happen if x equals 5). If, on the other hand, x does not have the value 5, the compiler will not execute the empty statement (still no effect) and will continue as before to assign the value 3 to y (which is not what you wanted to have happen unless x equals 5). In other words, the if statement doesn't matter; y is going to get the value 3 regardless.

The simplest form of selection which selects between two alternatives. If its condition is true, the first

statement is executed; otherwise, the second statement is.

int main()

{

   int a=0;

   int b=0

   cout<< "Please enter two integers\n";

   cin>>a>>b;

   if (a<b)

      cout<<"max("<<a<<","<<b<<") is "<<b<<"\n";

   else 

      cout<<"max("<<a<<","<<b<<") is "<<a<<"\n";

}

What is wrong with this code?

int main()

{

   const double cm_per_inch = 2.54;

   int length = 1;

   char unit = 0;

   cout<<"please enter a lenth followed by a unit (c or i):\n";

   cin<<length<<unit;

   if (unit == 'i')

      cout <<length<<"in ==" <<cm_per_inch*length<<"cm\n";

   else

      cout <<length<< "cm ==" <<length/cm_per_inch<<"in\n";

}

if (expression) statement

else statement

if (expression) statement

else if (expression) statement

else statement

1. The value on which we switch must be of an integer, char, or enumeration type. In panicular, you cannot switch on a string.

2. The values in the case labels must be constant expressions. In particular, you cannot use a variable in a case label.

3. You cannot usc the same value for two case labels.

4. You can use several case labels for a single case.

5. Each case ends with a break.

What is wrong with this switch statement based code?

int main()

{

   cout<<"Do you like fish?\n";

   string s;

   cin>>s;

   switch (s) {

   case "no";

   //...code here

   case "yes";

      break;

   //...code here 

      break;

   }

}

What's wrong with this code?

int main()

{

   int y='y';

   const char n='n';

   const char m='?'

   cout<<"Do you like fish?\n";

   char a;

   cin>>a;

   switch (a) {

   case "n";

      //...code here

       break;

   case "y";

      //...code here 

      break;

   case "m";

      //...code here 

      break;

   case "n";

      //...code here 

      break;

   default:

      //

      break;

   }

}

There is a duplicate case label (n's value is 'n')

There is a variable in the case label, int y instead of char y. 

int main()

{

   cout<< "Please enter a digit\n";

   char a;

   cin>>a;

   switch(a){

   case '0': case '2': case '4': case '6': case '8':

      cout<< "is even\n";

      break;

   case '1': case'3': case '5': case '7': case '9':

      cout<< "is odd\n";

      break;

   default:

      cout<<"is not a digit\n"

      break;

   }

}

Whats wrong with this code?

int main()

{

   const double cm_per_inch=2.54;

   int length=1;

   char unit='a';

   cout<<"please enter a length followed by a unit (c or i):\n";

   cin>>length>>unit;

   switch (unit) {

   case 'i':

      cout<<length<<"in=="<<cm_per_inch*length<<"cm\n";

   case 'c':

      cout<<length<<"cm=="<<length/cm_per_inch<<"in\n";

   }

} 

A compiler will accept this, and when you have finished case 'i' you'll just "drop through" into case 'c', so that if you enter 2i the program will output

2in == 5.08cm

2cm == 0.787402 in

Identify this code:

int main()

{

   int i=0
   while (i<100){

      cout<<i<<'\t' << square(i)<<'\n';

      ++i;

    }

} 

and initializer for the loop variable

A way to repeat the statement (while)

A termination criterion

a variable to keep track of how many times we have been through the loop (a loop variable/control variable)

The loop body, delimited by curly braces, that writes out something to do each time around the loop.

int main()

{

   for (int i=0; i<100; ++i)

      cout<<i<<'\t'<<square(i)<<'\n';

}

What is wrong with this code?

int main()

{

   for (int i=0; i<100; ++i){

      cout<<i<<'\t'<<square(i0<<'\n';

      ++i;

   }

}

the ++i at the end of the body ensures that i is incremented twice, so instead of giving the squares of 100 values, it will give the squares of the 50 even values of i.

int square(int x)

{

   return x*x

}

What does this function do?

int square(int x)

{

   return x*x

}

How could this function be used in another function?

int square(int x)

{

   return x*x

}

int main()

{

   cout<<square(2)<<'\n';       //prints 4

   cout<<square(10)<<'\n';      //prints 100

} 

Why would the following functions return an error?

square(2);

int v1 = square();

int v2 = square;

int v3 = square (1,2)

int v3 = square("two")

unused return value

argument missing

parethesis missing

too many arguments

wrong type of argument, int expected

When a function takes no argument and returns no value. 

ex.

void write_sorry()

{   

   cout << "sorry\n";

}

Makes the computation logically separate

Makes the program text clearer (by naming the computation)

Makes it possible to use the function in more than one place in our program

Eases testing

What do these functions do?

void print_square(int v)

{

   cout<<v<<'\t'<<v*v<<'\n';

}

int main()

{

   for (int i=0; i<100; ++i) print_square(i)

}

print_square performs two logically seperate actions. It prints and it calculates a square. Then, main calls the print_square function in a form loop so long that i<100.

This program is of poor design, because it is generally better for a function to perform only one action, whereas print_square performs two. 

a way of supplying that information separate

from the complete function definition.

ex.

int square(int);         //declaration of square

double sqrt(double);  //declaration of sqrt

A vector is simply a sequence of elements that you can access by index. Vectors start at 0, so for example, if we had

vector<int>v(6)

we have a vector that stores integers into six slots, 0-5. 

example:

vector<int>v(6);

v[0] =#;

v[1] =#;

v[2] =#;

v[3] =#;

v[4] =#;

v[5] =#;

Through what numbers would this vector be able to store elements?

vector<string>philosopher(4)

an operation that adds a new element to a vector. 

example: 

vector<double>v;

v.push_back(5.6);

v.push_back(7.9);

this would end with the vector v having 2 elements, 

v[0]==5.6

v[1]==7.9

a member function call. Push_back is a member function cvector and must be called using the dot notation:

object_name.member-function-name (argument list)

What does this code do?

int main()

{

   vector<double>temps;

   double temp;

   while(cin>>temp)

   temps.push_back(temp);

   //...do something

}

first a vector is declared to hold data and a variable into which we can read each number as it comes in. It will read and store only doubles.

While the user is inputting numbers, they may continue input until they break the loop by inputting something else. 

These doubles (temp) are pushed back into the temps vector.

Now we can do whatever we want with the information we've gained. 

for (int i=0; i<v.size(); ++i);

   cout<<"v["<<i<<"]=="<<v[i]<<'\n';

Identify what every aspect of this code dose. 

int main()

{

   vector<double>temps;

   double temp;

   while(cin>>temp)

   temps.push_back(temp);

   double sum=0;

   for (int i=0; i<temps.size(); ++i) sum+=temps[i]

   cout<<"average temperature: " <<sum/temps.size()<< endl; 

   sort(temps.begin(),temps.end());

   cout<<"Median temperature: "<<temps[temps.size()/2]<<endl;

}

first a vector is declared to hold data and a variable into which we can read each number as it comes in. It will read and store only doubles.

While the user is inputting numbers, they may continue input until they break the loop by inputting something else. 

These doubles (temp) are pushed back into the temps vector.

now, for i>the number of elements in temps, the fpr loop will continue. sum is equal to (0+the number of elements in the vector).

The function now outputs the average temperature by dividing the sum of all of the elements by the number of vector elements. 

Now the member call function sorts the temperatures from beginning to end.

Now the function outputs the median temperature, which is the element number that is equal to temps.size()/2 (because that calculates the number that is in the exact middle of the list of the vector elements)

What does this program do?

int main()

{

   vector<string>words;

   string temp;

   while (cin>>temp)

      words.push_back(temp);

   cout<<"Number of words: " <<words.size()<<endl;

   sort(words.begin(),words.end());

   for (int=0 || words[i-1]!=words[i])

      cout<<words[i]<<"\n";

}

It takes in string elements into the vector words, outputs the number of words you input, and then sorts the words from beginning to end (alphabetical order). Then it outputs all of the words you typed in without repeated words; however there was no way coded to stop the input stream of cin>>temp, so the user has to use ctrl+z to stop the input stream. 

The line

if (i==0 || words[i-1]!=words[i]) 

is what is used to check and see if the previous word is the same as the next word. 

Errors found by the compiler. We can further classify

compile-time errors based on which language rules they violate, for example:

Syntax errors

Type errors

Errors found by the linker when it is trying to combine

object files into an executable program.

Errors found by checks in a ru nning program. We can

further classify run-time errors as:

Errors detected by the computer (hardware and/or operating system)

Errors detected by a library

Errors detected by user code

Organize software to minimize errors.

Eliminate most of the errors we made through debugging and testing.

Make sure the remaining errors are not serious.

If we are not specific about what a program should do,

we are unlikely to adequately examine the "dark corners" and make sure that all cases are handled (i.e., that every input gives a correct answer or an adequate error message).

During development, there are obviously cases that

we haven't yet taken care of. That's unavoidable. What we must aim for is to know when we have handled all cases.

Functions take arguments. If a function is given an

argument we don't handle, we have a problem. An example is calling the standard library square root function with - 1.2: sqrt(-1.2). Since sqrt()

of a double returns a double, there is no possible correct return value.

Programs typically read data (from a keyboard. from

files, from GUls, from network connections, etc.). A program makes many assumptions about such input, for example, that the user will input a number. What if the user inputs "aw, fudge!" rather than the expected integer? 

what kind of error are these?

int s1=area(7;

int s1=area(7)

Int s2=area(7):

What kind of errors are these?

int x0=arena(7);

int x1=area(7);

int x2=area("seven",2);

Type errors.

In order:

undeclared function

wrong number of arguments

1st argument has wrong type

What kind of errors are these?

int x4=area(10,-7)

int x5=area(20.6,9.3)

char x6=area(100,9999)

They are known as non errors because the compiler won't return an error message. In order, the problems these have are: 

Logically, you can't have a rectangle with a width of -7

the area function only uses ints, so it would call area(20,9)

it will be assigned to a char, causing the compiler to truncate the result, resulting in the output -36.

What kind of error would this program give? 

int area(int length , int width); 

int main()

{

int x= area(2,3);

}

It means that the program itself will protect the call of the function in main. for example:

area is a function in a library where we can't modify it.

if (x<=0) error("non-positive x");

if (y<=0) error("non-positive y");

int area1 = area(x,y);

Why is the following code wrong?

int area(int x, int y){ .... }

.....

double area(double x, double y)

The area function only calculates the area of ints, as defined earlier. Functions with the same name but different types will not match and will be

ignored.

What is wrong with this program?

int area(int length, int width)

{

   return length*width ;

}

int framed_area(int x, int y)

{

   return area(x-2,y-2);

}

int main()

{

   int x= -1;

   int y = 2;

   int z = 4;

   //...

   int area = area(x,y);

   int area1 = framed_area(1,z);

   int area3 = framed_area(y,z);

   double ratio = double(area1)/area3; 

}

these calls lead to negative values, representing areas, being assigned to area1 and area2.

area3 will be 0, so that double(area1)/area3 divides by zero. this leads to a hardware-detected error that teminates the program with some

cryptic message relating to hardware.

It means that the function itself does the error checking, instead of the other function that calls it.

sometimes we can't modify the function definition

sometimes the called function doesn't know what to do in case of an error

sometimes the called function doesnt know where it was called from

Sometimes adding checks to every function causes performance loss, or raises the cost of a program.

In this program, what is doing the error checking?

char ask_user(string question)

{

cout « question « "? (yes or no)\n";

string answer = " ";

cin»answer;

if (answer =="y" || answer=="yes") return 'y';

if (answer =="n" || answer==" no") return 'n';

return 'b'; 

}

Now both the called function and all callers must test. The caller hasonly a simple test to do but must still write that test and decide what to do if it fails.

A caller can forget to test. That can lead to unpredictable behavior further along in the program.

The basic idea is that if a function finds an error that it cannot handle, it does not return normally; instead, it throws an exception indicating what went wrong.

Any direct or indirect caller can catch the exception, that is, specify what to do if the called code used throw. A function expresses interest in exceptions by using a try block listing the kinds of exceptions it wants to handle in the catch parts of the try block. if no caller catches an exception, the program terminates. 

What is this?

class Bad_area {};

What does this code do?

class Bad_area {};

 int area(int length, int width)

{

   if (length<=0 || width<=0) throw Bad_area();

   return length*width;

}

What does this code do?

int main()

try {

      int x=-1

      int y=2

      int z=4

      //.... code here

      int area1 = area(x,y);

      int area2 = framed_area(1,z)

      int area3 = framed_area(y,z)

      double ratio = area1/area3;

}

catch (Bad_area) {

      cout<<"Oops! Bad arguments to area()\n";

}

What error is caused by this code, and why?

vector<int>v;

int i;

while (cin>>i) v.push_back(i)

for (int i=0; i<=v.size(); ++i)

   cout<<"v["<<i<<"]=="v[i]<<endl;

the termination condition is i<=v.size() rather than the correct i<v.size(). This has the unfortunate

consequence that if we read in five integers we' ll try to write out six. We try to read v[5], which is one beyond the end of the vector.

the index was not within the limits (bounds)

of the vector.

What is the error caused by this code?

vector<int> v[5];

inl x = v[5];

if (cin) {

//all is well

}

else {

didnt succeed, do something else

}

double some_function()

{

   double d=0;

   cin>>d;

   if (!cin) error("couldn't read a double in 'some function()'");

}

When we deal with a runtime error, we simply want to catch it. so...

void error(string s)

{

   throw runtime_error(s)

}

int main()

try {

//our program

return 0;

}

catch (runtime_error& s){

   cerr<<"runtime error: "<<s.what()<<'\n';

keep_window_open()

return 1;

}

No, so catching runtime_error does not deal with the out_of range errors that we might get from misuse of

vectors and other standard library container types. However, both out_of_range

and runtime_error are "exceptions," So we can catch exception to deal with both:

int mainO

try {

                        // our program

return 0;            // 0 indicates success

}

catch (exception& e) {

cerr « "error:«e.what()« '\n ';

keep_window_open();

return 1;           // 1 indicates failure

}  

catch ( ... ){

cerr « "Oops: unknown exception!\n " ;

keep_window_open();

return 2;               //2 indicates failure

}

What does this code do?

void error(string s1, string s2)

{

throw runtime_error(s1 +s2);

{

it is a runtime_error exception that throws an exception is an assignment or initialization would lead to a changed value. We use narrow cast when we need to convert a value and we are not sure if it will fit. It is defined in std_lib_facilities.h and implemented using error(). the word cast means type conversion.

ex.

int x1 = narrow_cast<int>(2.9)   //Gets thrown

int x2 = narrow_cast<int>(2.0) //is ok

What is the logical error in this code?

int main()

{

   vector<double> temps;

   double temp = 0;

   double sum = 0;

   double high_temp = 0;

   double low_temp = 0;

   while (cin» temp) 

      temps. push_back(temp);

   for (int i = 0; i<temps.size(); ++i)

   {

      if(temps[i] > high_temp) high_temp = temps[i];

      if(temps[i] < low_temp) low_temp = temps[i];

      sum += temps[i];

    }

   cout « "High temperature: " « high_temp« endl;

   cout « "Low temperature : " « low_temp« endl;

   cout « "Average temperature: " « sum/temps.size() « endl;

}

If you have to deal with a set of temperatures that does not have a low temp that is below 0, it will not change the initialization of low temp to the new temp.

If all of the temperatures are below zero, the intitalization for high temp would be the same problem.

What is the logical error in this code?

int main()

{

   vector<double> temps;

   double temp = 0;

   double sum = 0;

   double high_temp = -1000;

   double low_temp = 1000;

   while (cin» temp) 

      temps. push_back(temp);

   for (int i = 0; i<temps.size(); ++i)

   {

      if(temps[i] > high_temp) high_temp = temps[i];

      if(temps[i] < low_temp) low_temp = temps[i];

      sum += temps[i];

    }

   cout « "High temperature: " « high_temp« endl;

   cout « "Low temperature : " « low_temp« endl;

   cout « "Average temperature: " « sum/temps.size() « endl;

}

The act of deliberately searching for errors and removing them. It usually works like...

1. Get the program to compile.

2. Get the program to link.

3. Get the program to do what it is supposed to do.

while {the program doesn't appear to work) {      // pseudo code

   Randomly look through the program for something that "looks odd"

   Change it to look better

}

What requirement is a compiler going to catch here?

int x = my_complicated_function(1, 2, "horsefeathers");

Here, the compiler will catch that the requirement ("precondition") that the third

argument be an integer was violated.

What conditions are checked in this program? What happens to these checked conditions? 

//calculate area of a rectangle;

// throw a Bad_area exception in case of a bad argument

int area(int length, inl width)

{

if (length<=0 || width <=0) throw Bad_area();

return length*width;

 }

int area(int length, int width)

}

if (length<=-0 || width <=0) error("area() pre-condition");

int a = length*width;

if (a<=0) error("area() post-condition");

return a;

}

What conditions are checked in this program? What happens to these checked conditions? 

 preconditions: length and width are positive

 post-condition: returns a positive value that is the area

A requirement of a function upon its argument.

 int my_complicated_funclion (int a, int b, int c)

// the arguments are positive and a < b < c

{

if (!(0<a && a<b && b<c»))

error("bad arguments for mcf") ;

//...

}