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Numeric Types, Expressions, and Output
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Chapter 3 Topics Constants of Type int and float Evaluating Arithmetic Expressions Implicit Type Coercion and Explicit
Type Conversion Calling a Value-Returning Function Using Function Arguments Using C++ Library Functions in
Expressions Calling a Void Function C++ Manipulators to Format Output String Operations length, find, and
substr
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C++ Data TypesC++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
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C++ Simple Data TypesC++ Simple Data Types
simple types
integral floating
char short int long bool enum float double long double
unsigned
Standard Data Types in C++Integral Types
represent whole numbers and their negatives
declared as int, short, or longFloating Types
represent real numbers with a decimal point
declared as float or doubleCharacter Type
represents single charactersdeclared as char
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Samples of C++ Data Valuesint sample values
4578 -4578 0
float sample values95.274 95. .2659521E-3 -95E-1 95.213E2
char sample values
‘B’ ‘d’ ‘4’ ‘?’ ‘*’
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7
2.7E4 means 2.7 x 10 4 =
2.7000 =
27000.0
2.7E-4 means 2.7 x 10 - 4 =
0002.7 =
0.00027
More About Floating Point Values
Floating point numbers have an integer part and a fractional part, with a decimal point in between. Either the integer part or the fractional part, but not both, may be missing
Examples 18.4 500. .8 -127.358
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More About Floating Point Values Alternatively, floating point values can
have an exponent, as in scientific notation--the number preceding the letter E doesn’t need to include a decimal point
Examples 1.84E1 5E2 8E-1 -.127358E3
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Division OperatorThe result of the division operator depends
on the type of its operands
If one or both operands has a floating point type, the result is a floating point type. Otherwise, the result is an integer type
Examples11 / 4 has value 211.0 / 4.0 has value 2.7511/ 4.0 has value 2.75
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/*******************************************************FreezeBoil programThis program computes the midpoint between the freezing and boiling points of water*******************************************************/#include < iostream >using namespace std;const float FREEZE_PT = 32.0; // Freezing point of waterconst float BOIL_PT = 212.0; // Boiling point of waterint main(){ float avgTemp; // Holds the result of averaging // FREEZE_PT and BOIL_PT cout << “Water freezes at “ << FREEZE_PT << endl; cout << “ and boils at “ << BOIL_PT << “ degrees.” << endl; avgTemp = FREEZE_PT + BOIL_PT; avgTemp = avgTemp / 2.0; cout << “Halfway between is “; cout << avgTemp << “ degrees.” << endl; return 0;}
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Function main Continued cout << “Water freezes at “ << FREEZE_PT << endl; cout << “ and boils at “ << BOIL_PT << “ degrees.” << endl;
avgTemp = FREEZE_PT + BOIL_PT; avgTemp = avgTemp / 2.0;
cout << “Halfway between is “; cout << avgTemp << “ degrees.” << endl;
return 0;}
Modulus OperatorThe modulus operator % can only
be used with integer type operands and always has an integer type result
Its result is the integer type remainder of an integer division
Example: 11 % 4 has value 3
because13
)4 11
2 R = 3
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More C++ Operators
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int age;
age = 8;
age = age + 1;
age
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age
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Prefix FormIncrement Operator
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int age;
age = 8;
++age;
age
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age
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Postfix Form Increment Operator
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int age;
age = 8;
age++;
age
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age
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Decrement Operator
100
int dogs;
dogs = 100;
dogs--;
dogs
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dogs
Which Form to UseWhen the increment(or decrement)
operator is used in a “stand alone” statement solely to add one(or subtract one) from a variable’s value, it can be used in either prefix or postfix form
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dogs--; --dogs;
USE EITHER
BUT...When the increment(or decrement)
operator is used in a statement with other operators, the prefix and postfix forms can yield different results
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We’ll see how later . . .
What is an Expression in C++?An expression is a valid
arrangement of variables, constants, and operators
In C++ each expression can be evaluated to compute a value of a given type
The value of the expression 9.3 * 4.5 is 41.85
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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++ OperatorsPrecedence Operator Description Higher ( ) Function call + Positive - Negative * Multiplication / Division % Modulus
(remainder)
+ Addition - SubtractionLower = Assignment
PrecedenceHigher Precedence determines
which operator is applied first in an expression having several operators
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AssociativityLeft 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) - 14 – 1 =
3 24
Evaluate the Expression7 * 10 - 5 % 3 * 4 + 9
(7 * 10) - 5 % 3 * 4 + 9 70 - 5 % 3 * 4 + 9
70 - (5 % 3) * 4 + 9 70 - 2 * 4 + 9 70 - ( 2 * 4) + 9 70 - 8 + 9 (70 - 8 ) + 9
62 + 971
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ParenthesesParentheses can be used to change the
usual orderParts in() are evaluated firstEvaluate
(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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Recall Assignment Operator SyntaxVariable = Expression
First, Expression on right is evaluatedThen the resulting value is stored in the
memory location of Variable on left
NOTE: An automatic type coercion occurs after evaluation but before the value is stored if the types differ for Expression and Variable
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What value is stored?float a;
float b;
a = 8.5;
b = 9.37;
a = b;
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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
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Type Casting is Explicit Conversion of Typeint(4.8) has value 4
float(5) has value 5.0
float(7/4) has value 1.0
float(7) / float(4) has value1.75
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Some Expressionsint age;
Example Valueage = 8 8- age - 85 + 8 135 / 8 06.0 / 5.0 1.2float(4 / 8) 0.0float(4) / 8 0.5
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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
hiCost
12.35
loCost
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Using Predefined FunctionsA function (subprogram): set of instructions
When activated, it accomplishes a task
main executes when a program is run
Other functions execute only when called
C++ includes a wealth of functions
Predefined functions are organized as a collection of libraries called header files
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Predefined FunctionsHeader file may contain several functions
To use a predefined function, you need the name of the appropriate header file
You also need to know:Function name
Number of parameters required
Type of each parameter
What the function is going to do
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Predefined Function ExampleTo use pow (power), include cmath
pow has two numeric parameters
The syntax is: pow(x,y) = xy
x and y are the arguments or parameters
In pow(2,3), the parameters are 2 and 3
HEADER FILE FUNCTION EXAMPLE VALUE OF CALL
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fabs(x) fabs(-6.4) 6.4
<cmath> pow(x,y) pow(2.0,3.0) 8.0
<cmath> sqrt(x) sqrt(100.0) 10.0
<cmath> log(x) log(2.0) .693147
sqrt(x) sqrt(2.0) 1.41421
<cstdlib> abs(i) abs(-6) 6
Write C++ Expressions forThe 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)39
Manipulators Manipulators are used only in input
and output statements
endl, fixed, showpoint, 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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Using ManipulatorsFixed and Showpointuse the following statement 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 << fixed << showpoint; 41
setprecision(n)Requires #include <iomanip> and
appears in an expression using insertion operator(<<)
If fixed has already been specified, argument n determines 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> // For setw() and setprecision()#include <iostream>
using namespace std;
int main(){ float myNumber = 123.4587; cout << fixed << showpoint; // Use decimal format // Print decimal points 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
Manipulator setw
“Set width” lets us control how many character positions the next data item should occupy when it is output
setw is only for formatting numbers and strings, not char type data
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setw(n)Requires #include <iomanip> and appears in
an expression using insertion operator(<<)
Argument n is called the fieldwidth specification, and determines the number of character positions in which to display a right-justified number or string(not char data); the number of positions used is expanded if n is too narrow
“Set width” affects only the very next item displayed and is useful to align columns of output 46
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What is exact output?#include <iomanip> // For setw()#include <iostream>#include <string>
using namespace std;
int main(){ int myNumber = 123; int yourNumber = 5;
cout << setw(10) << “Mine” << setw(10) << “Yours” << endl
<< setw(10) << myNumber << setw(10) << yourNumber << endl;
return 0;}
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Output
12345678901234567890 Mine Yours 123 5
Each is displayed right-justified andeach is located in a total of 10 positions
position
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What is exact output?#include <iomanip> // For setw() and setprecision()#include <iostream>
using namespace std;
int main(){ float myNumber = 123.4; float yourNumber = 3.14159;
cout << fixed << showpoint; // Use decimal format; print decimal points 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 positions with 4 places after the decimal point
12345678901234567890
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float x = 312.0; float y = 4.827;
cout << fixed << 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
More Examplesx
312.0
y
4.827
setfillUsed to fill the unused columns with a
character other than a space when used with the setw manipulator.
cout << setfill(‘*’);cout << setw(5) << 15 << setw(7) << 7634
<< setw(8) << “Warm” << endl;
Output:***15***7634****Warm
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Left and right maniulatorsDefault setting is that output is right justified
when using setw.To change to left, use
cout << left;Output is then left justified until changed.To change back to right, use
cout << right;
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HEADER MANIPULATOR ARGUMENT EFFECT FILE TYPE
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<iostream> showpoint none displays decimal point
<iostream> fixed none suppresses scientific notation
<iomanip> setprecision(n) int sets precision to n digits
<iomanip> setw(n) int sets fieldwidth to n positions
<iostream> endl none terminates output line
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Formatting Outputendl manipulator moves output to the
beginning of the next line
setprecision(n) outputs decimal numbers with up to n decimal places
fixed outputs floating-point numbers in a fixed decimal format
showpoint forces output to show the decimal point and trailing zeros
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Types of ManipulatorsTwo types of manipulators:
With parameters
Without parameters Parameterized: require iomanip header
setprecision, setw, and setfill
Nonparameterized: require iostream headerendl, fixed, showpoint, left, right
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I/O and the string TypeAn input stream variable (cin) and
extraction operator >> can read a string into a variable of the data type string
Extraction operatorSkips any leading whitespace characters
and reading stops at a whitespace character Should not be used to read strings with
blanksThe function getline
Reads until end of the current lineShould be used to read strings with blanks
getline(cin, mystring);
The string TypeTo use the data type string, the program
must include the header file <string>The statement:
string name = "William Jacob";
declares name to be a string variable and also initializes name to "William Jacob"
The first character, 'W', in name is in position 0; the second character, 'i', is in position 1, and so on
The string Type (continued)The variable name is capable of storing any
size stringBinary operator + (to allow the string
concatenation operation), and the array subscript operator [], have been defined for the data type string
For example, If str1 = "Sunny", the statement stores the string "Sunny Day" into str2:
str2 = str1 + " Day";
length FunctionLength returns the number of characters
currently in the stringThe syntax to call the length function is:
strVar.length()
where strVar is variable of the type stringlength has no argumentslength returns an unsigned integerThe value returned can be stored in an
integer variable
size FunctionThe function size is same as the function length
Both functions return the same valueThe syntax to call the function size is:
strVar.size()
where strVar is variable of the type stringAs in the case of the function length, the
function size has no arguments
find Functionfind searches a string for the first
occurrence of a particular substringReturns an unsigned integer value of type string::size_type giving the result of the search
The syntax to call the function find is:strVar.find(strExp)
where strVar is a string variable and strExp is a string expression evaluating to a string
The string expression, strExp, can also be a character
find Function (continued)If successful, find returns the position in strVar where the match begins
For the search to be successful the match must be exact
If unsuccessful, find returns the special value string::npos (“not a position within the string”)
substr Functionsubstr returns a particular substring of a
string
The syntax to call the function substr is:
strVar.substr(expr1,expr2)
where expr1 and expr2 are expressions evaluating to unsigned integers
substr Function (continued)The expression expr1 specifies a position
within the string (starting position of the substring)
The expression expr2 specifies the length of the substring to be returned
swap Functionswap interchanges the contents of two
string variablesThe syntax to use the function swap is
strVar1.swap(strVar2);
where strVar1 and strVar2 are string variables
Suppose you have the following statements:string str1 = "Warm";
string str2 = "Cold";
After str1.swap(str2); executes, the value of str1 is "Cold" and the value of str2 is "War"
String summaryA string is a sequence of zero or more charactersStrings in C++ are enclosed in double quotation
marksThe function length returns the number of characters
currently in the string
The function size returns the number of characters currently in the string
The function find searches a string to locate the first occurrence of a particular substring
The function substr returns a particular substring of a string
The function swap is used to swap the contents of two string variables 70