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Programming in C++

Chapter 3

Arithmetic Expressions, Function Calls, and Output

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What is an Expression in C++?

An expression is any valid combination of operators and operands.

In C++ each expression has a value.

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Operators can be

binary involving 2 operands 2 + 3

unary involving 1 operand - 3

ternary involving 3 operands later

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Some C++ Operators

Precedence Operator Description Higher ( ) Function call

+ Positive

- Negative

* Multiplication

/ Division % Modulus

(remainder)

+ Addition

- Subtraction

Lower = Assignment

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Precedence

Higher Precedence determines which operator is applied first in an expression having several operators.

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Associativity

Left to right Associativity means that in an expression having 2 operators with the same priority, the left operator is applied first.

In C++ the binary operators

* , / , % , + , - are all left associative.

Expression 9 - 5 - 1 means ( 9 - 5 ) - 1

4 - 1

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7 * 10 - 5 % 3 * 4 + 9means (7 * 10) - 5 % 3 * 4 + 9

70 - 5 % 3 * 4 + 970 - (5 % 3) * 4 + 9 70 - 2 * 4 + 9 70 - ( 2 * 4 ) + 9 70 - 8 + 9 ( 70 - 8 ) + 9

62 + 9 71

Evaluate the Expression

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Parentheses Parentheses can be used to change the

usual order Parts in ( ) are evaluated first Evaluate (7 * (10 - 5) % 3) * 4 + 9

( 7 * 5 % 3 ) * 4 + 9

( 35 % 3 ) * 4 + 9 2 * 4 + 9

8 + 9 17

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VariableName = Expression

First, Expression on right is evaluated.

Then the resulting value is stored in the memory location of VariableName on left.

NOTE: An automatic type coercion occurs after evaluation but before the value is stored if the types differ for Expression and VariableName

Assignment Operator Syntax

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What value is stored?

float A;

float B;

A = 8.5;

B = 9.37;

A = B;

A

B

A

B

8.5

9.37

?

?

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What is stored?

?float SomeFloat;

SomeFloat

SomeFloat = 12; // causes implicit type conversion

SomeFloat

12.0

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What is stored?

?int SomeInt;

SomeInt

SomeInt = 4.8; // causes implicit type conversion

SomeInt

4

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Type Casting is Explicit Conversion of Type

int(4.8) has value 4

float(5) has value 5.0

float(7/4) has value 1.0

float(7) / float(4) has value 1.75

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<iostream.h> is header file

for a library that defines 3 objects

an istream object named cin (keyboard)

an ostream object named cout (screen)

an ostream object named cerr (screen)

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No I/O is built into C++

Instead, a library provides input stream and output stream

Keyboard Screenexecutingprogram

istream ostream

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>> is a binary operator

>> is called the input or extraction operator

>> is left associative

EXPRESSION HAS VALUE

cin >> Age cin

STATEMENT

cin >> Age >> Weight ;

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<< is a binary operator

<< is called the output or insertion operator

<< is left associative

EXPRESSION HAS VALUE

cout << Age cout

STATEMENT

cout << “You are “ << Age << “ years old\n” ;

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Some Expressionsint Age;

EXAMPLE VALUE

Age = 8 8- Age - 85 + 8 135 / 8 06.0 / 5.0 1.2float ( 4 / 8 ) 0.0float ( 4 ) / 8 0. 5cout << “How old are you?” coutcin >> Age cincout << Age cout

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What values are stored?

float LoCost;

float HiCost;

LoCost = 12.342;

HiCost = 12.348;

LoCost = float (int (LoCost * 100.0 + 0.5) ) / 100.0;

HiCost = float (int (HiCost * 100.0 + 0.5) ) / 100.0;

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Values were rounded to 2 decimal places

12.34

LoCost

HiCost

12.35

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Functions

Every C program must have a function called main ( )

Program execution always begins with function main ( )

Any other functions are subprograms and must be called.

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What is in a block?

{

0 or more statements here

}

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Function Calls

One function calls another by using the name of the called function together with ( ) containing a parameter list

A function call temporarily transfers control from the calling function to the called function

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Parts of a Function

Every function has 2 parts

int main (void) heading{

body block return 0;

}

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What is in a heading?

int main (void)

type of returned valuename of function

says no parameters

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More about functions

It is not considered good practice for the body block of main ( ) to be long.

Function calls are used to do tasks

Every C++ function has a return type

If the return type is not void, the function returns a value to the calling block.

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Where are functions?

located in libraries

OR

written by programmers

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HEADER FILE FUNCTION EXAMPLE VALUE OF CALL

fabs(x) fabs(-6.4) 6.4

<math.h> pow(x,y) pow(2.0,3.0) 8.0

<math.h> sqrt(x) sqrt(100.0) 10.0

<iomanip.h> setprecision(n) setprecision(3)

<math.h> log(x) log(2.0) .693147

sqrt(x) sqrt(2.0) 1.41421

<stdlib.h> abs(i) abs(-6) 6

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Write C++ Expressions for

The square root of b2 - 4ac

sqrt ( b * b - 4.0 * a * c )

The square root of the average of MyAge and YourAge

sqrt ( (MyAge + YourAge) / 2 )

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Manipulators

Manipulators are used only in input and output statements.

endl, setw, and setprecision are manipulators that can be used to control output format.

endl is use to terminate the current output line, and create blank lines in output.

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Insertion Operator ( << )

The insertion operator << takes 2 operands.

The left operand is a stream expression, such as cout.

The right operand is an expression of simple type, or a string, or a manipulator.

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Output Statements

SYNTAX (revised)

cout << ExprOrStringOrManipulator << ExprOrStringOrManipulator . . . ;

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setprecision(n)

requires #include <iomanip.h> and appears in an expression using insertion operator (<<)

specifies n as the number of places displayed after the decimal point for floating point values

remains in effect until explicitly changed by another call to setprecision

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What is exact output?

#include <iomanip.h>#include <iostream.h>

int main ( void){ float myNumber = 123.4587 ;

cout.setf ( ios::fixed , ios::floatfield ) ; // use decimal format cout.setf ( ios::showpoint ) ; // print decimal point

cout << “Number is ” << setprecision ( 3 ) << myNumber << endl ;

return 0 ;}

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OUTPUT

Number is 123.459

value is rounded if necessary to be displayed with exactly 3 places after the decimal point

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To Remember

To cause your program to output numbers that have a decimal point to a certain number of decimal places» cout.setf(ios::fixed);» cout.setf(ios::showpoint);» cout.precision(2);

Any output after these statements will have the precision as indicated

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setw(n) requires #include <iomanip.h> and appears in

an expression using insertion operator (<<)

affects only the very next item displayed

“set width” specifies n as the number of total columns in which to display a number or string (not char data). Parameter n is called the fieldwidth specification. The number of columns used is expanded if n is too narrow.

is useful to align columns of output

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What is exact output?

#include <iomanip.h>#include <iostream.h>int main ( void){ float myNumber = 123.4 ; float yourNumber = 3.14159 ;

cout.setf ( ios::fixed , ios::floatfield ) ; // use decimal format cout.setf ( ios::showpoint ) ; // print decimal point

cout << “Numbers are: ” << setprecision ( 4 ) << endl << setw ( 10 ) << myNumber << endl

<< setw ( 10 ) << yourNumber << endl ;

return 0 ;}

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OUTPUT

Numbers are: 123.4000 3.1416

each is displayed right-justified androunded if necessary and each islocated in a total of 10 columns with 4 places after the decimal point

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Using setf( )

setf( ) is a function associated with output streams. To call this function use this syntax

DesiredOutputStream.setf( ParameterList ) ;

setf( ) can be used to print the decimal point (even if there are trailing zeros) for floating values that are output, and to specify that the value be printed with a fixed position decimal point (rather than in scientific notation).

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cout.setf( ) statements

Use the following statements to specify that (for output sent to the cout stream) decimal format (not scientific notation) be used, and that a decimal point be included (even for floating values with 0 as fractional part).

cout.setf( ios :: fixed, ios :: floatfield ) ;

cout.setf( ios :: showpoint ) ;

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More examples

float x = 312.0 ; float y = 4.827 ; cout.setf ( ios::fixed , ios::floatfield ) ; cout.setf ( ios::showpoint ) ; OUTPUT

cout << setprecision ( 2 ) << setw ( 10 ) << x << endl ’’’’312.00

<< setw ( 10 ) << y << endl ; ’’’’’’4.83

cout << setprecision ( 1 ) << setw ( 10 ) << x << endl ’’’’’312.0

<< setw ( 10 ) << y << endl ; ’’’’’’’4.8

cout << setprecision ( 5 ) << setw ( 7 ) << x << endl 312.00000

<< setw ( 7 ) << y << endl ; 4.82700

x

312.0

y

4.827

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Program with several functions

main( ) function

Square( ) function

Cube( ) function

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Value-returning functions

#include <iostream.h>

int Square ( int ) ; // declares these 2 functionsint Cube ( int ) ;

int main ( void ){ cout << “The square of 27 is “

<< Square (27) << endl ; // function call cout << “The cube of 27 is “ << Cube (27) << endl ; // function call

return 0 ;}

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Rest of Program

int Square ( int n ) // header and body here{ return n * n ;}

int Cube ( int n ) // header and body here{ return n * n * n ;}

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A void function call stands alone

#include <iostream.h>

void DisplayMessage ( int n ) ; // declares function

int main(void){ DisplayMessage( 15 ) ; //function call cout << “Good Bye“ << endl ;

return 0 ;}

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A void function does NOT return a value

void DisplayMessage ( int n ) // header and body here{ cout << “I have liked math for “ << n << “ years” << endl ;}