1 chapter 6 the fundamental data types. 2 outline declarations and expressions fundamental data...

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Chapter 6

The Fundamental Data Types

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Outline

Declarations and expressionsFundamental data types

Characters and the data type char The Data type int and the integral types The floating types

The sizeof OperatorMathematical FunctionsConversions and Casts

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Declarations and Expressions

Declarations All variables must be declared before they

can be used. Why?

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Appropriate amount of space in memory should be set aside to each variable to hold its value

Declaration of a variable tells the compiler its data type.

Reason 1: Declarations enable the compiler to set aside an appropriate amount of space in memory to hold values associated with variables.

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Declarations and ExpressionsExample: applying division on different data types

int a=5, b=2, c=a/b; float a=5, b=2, c=a/b; Machine instructions used are different

Different machine instructions are used when an operator applied on different data types

Reason 2: Declarations enable the compile to instruct the machine to perform specified operations correctly.

The programmer need not be concerned about the difference, but the C compiler has to recognize the difference and give the appropriate machine instructions

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Declarations: Summary

All variables must be declared before they can be used.

o Tell the compiler to set aside an appropriate amount of space in memory to hold values associated with variables.

o Enable the compile to instruct the machine to perform specified operations correctly.

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Expressions Meaningful combinations of

constants, variables, and function calls.

Most expressions have both a value and a type

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Declarations and ExpressionsExamples of expressionsDeclarations: int a =12, b=10, c, d;Function min(int x, int y), returns the minimum value of x and y.

Examples of expressions: exp1, function call min(var1, var2): min(a,b) exp2, var * constant: a*12 exp3, function call min(exp1, exp2): min(min(a,b), a*12) exp4, exp3+exp1: min(min(a,b), a*12) +

min(a,b) exp5, var = exp3: c = min(min(a,b), a*12) exp6, var = exp5: d = c = min(min(a,b), a*12)

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Summary Declarations:

All variables must be declared before they can be used.

o Tell the compiler to set aside an appropriate amount of space in memory to hold values of variables.

o Enable the compile to instruct the machine to perform specified operations correctly.

ExpressionMeaningful combination of constants,

variables, and function calls.Most expressions have both a value and a

type

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Outline

Declarations and expressionsFundamental data types



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Integral types The types that can be used to hold integer

values.Characters: char, signed char, unsigned char short, int, long, unsigned short, unsigned, unsigned long

Floating types The types that can be used to hold real values.

float, double, long double

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Characters and the data Type char

Characters: Each char is stored in one byte of memory Variables of any integral type can be used

to represent characters.char, int

When a variable is used to read in characters and a test must be must be made for EOF, The variable should be of type int, not

char

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Exampleschar c=‘a’; /* ‘a’ has ASCII encoding 97 */int i=65; /* 65 is SCII encoding for ‘A’ */

printf(“%c”, c+1);/* b is printed */

printf(“%d”, c+2);/* 99 is printed */

printf(“%c”, i+3);/* D is printed */

Character codes for letters A through Z are contiguousCharacter codes for letters a through z are contiguous

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char, signed char, and unsigned char Each of the three char types is stored in one

byes, which can hold 28=256 distinct values.signed char : -128 to 127unsigned char : 0 to 255

Typically, char is equivalent to either signed char or unsigned char, depending on the compiler.

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Summary: Each char is stored in one byte of memory Variables of any integral type can be used to represent

characters. When a variable is used to read in characters and a test

must be must be made for EOF, The variable should be of type int, not chars

Each of the three char types is stored in one byes, which can hold 256 distinct values.signed char : -128 to 127unsigned char: 0 to 255char is equivalent to either signed char or unsigned

char, depending on the compiler.

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The Data Type int and the integral types

int Typically, an int is stored in a machine word. The length of a machine word is system-

dependentTwo bytes: 16 bits

o -215, -215+1, ……, -3, -2, -1, 0, 1, 2, 3, ……, 215-1

Four bytes: 32 bitso -231, -231+1, ……, -3, -2, -1, 0, 1, 2, 3, ……, 231-1

Integer overflow

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The Data Type int and the integral types

short, int, long storage provided for each type:

short <= int <= longsigned/unsigned

The integer values stored in an unsigned variable have no sign.

Example, If a variable of type unsigned int is stored

in 4 bytes,o range: 0, 1, ……, 232-1 o Compared to int: -231, ……, -2, -1, 0, 1, 2, ……,

231-1

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The Floating Types

Three floating types: float, double and long double

float: a floating constant with suffix Fo Example: 3.7F

double: no suffix, o Example: 3.7

long double: a floating constant with suffix L

o Example: 3.7L

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The Floating Types

Notation for floating constants: Decimal notation 12.0 Exponential notation:

Examples:o 1.2e5 = 1.2*105

o 1.2e-5 = 1.2*10-5

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The Floating Types

rules of exponential notation: No blank, no special characters (such as , ; ) Three parts: Integer Fraction Exponent

must contain either a decimal point or an exponential part or both

If a decimal point is present, either an integer part or fractional part or both must be present.

Otherwise, there must be an integer part along with an exponential part.

Example: 1.234e-5

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The Floating Types

Format of exponential notation: (cont’d) Example

3.13.1e-2F0e01.

But not3.1,131.e0-3.1 /* floating constant expression */

No blank, no special characters (such as , ; )either a decimal point or an exponential part or bothIf a decimal point is present, either an integer part or fractional part or both must be present.Otherwise, there must be an integer part along with an exponential part.

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The Floating Types

Three floating types: float, double and long double storage : float <= double <= long double Not all real numbers are representable.

Typically, a float: 10-38 to 10+38

a double: 10-308 to 10+308

Floating arithmetic operations, unlike the integer arithmetic operations, need not be exact.

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The Floating Types

Summary: Three floating types: float, double and long

doublestorage : float <= double <= long double

Notation of floating constant:Decimal notation: 123456.0Exponential notation: 1.23456e5

Not all real numbers are representable. Floating arithmetic operations, unlike the integer

arithmetic operations, need not be exact.

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Outline

DeclarationsFundamental data types



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The sizeof Operator

Operator: sizeof(object) Returns an integer that represents the number

of bytes needed to store the object in memory. An object can be

a type o into float,

An expression o a+b,

An array or structure type (introduced later)

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The sizeof Operator

Why Operator: sizeof(object)? The sizes of some fundamental types are

machine dependent, such as int. The sizeof operator provides precise

information about the store requirements for the fundamental types on a given machine.

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The sizeof Operator

Example#include <stdio.h>int main(void){ printf("Size of char: %3d byte \n", sizeof(char)); printf("Size of int: %3d byte \n", sizeof(int)); printf("Size of float: %3d byte \n", sizeof(float)); printf("Size of double: %3d byte \n", sizeof(double));}

% a.outSize of char: 1 byteSize of int: 4 byteSize of float: 4 byteSize of double: 8 byte

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The sizeof Operator

sizeof(….) is an operator, not a function If sizeof is being applied to a type,

parentheses are requiredExample: sizeof (int), but not

sizeof int Otherwise, parentheses are optional

Exampleo sizeof(a+b+7.7) sizeof a+b+7.7

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The sizeof Operator

Summary sizeof(object) Returns an integer that represents the number of

bytes needed to store the object in memory. An object can be

a type such as int or float,An expression such as a+b,An array or structure type (introduced later)

sizeof(….) is an operator, not a function If sizeof is being applied to a type,

o Parentheses are requiredOtherwise, parentheses are optional

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Outline




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Mathematical Functions

C System The C language The preprocessor The compiler The library

Contains many useful functions, such as file handles and mathematical functions.

Other tools, such as editors and debuggers

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There are no built-in mathematical functions in C language

Functions are available in the mathematics library. Examples of mathematical functions:

sqrt(), pow(), exp(), log(), sin(), cos(), tan()

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How to use the functions in the mathematics library? Provide function prototypes in the code

The function prototypes of mathematics functions are provided in file math.h

#include <math.h> In traditional C systems, the mathematics

library is often considered to be separate,The –lm option may be needed to compile

gcc –lm f.c

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Example

#include <math.h>main(){ double x = 0.81; printf("%.2f\n", sqrt(x));}

% gcc -lm m.c% a.out0.90%

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Summary There are no built-in mathematical functions

in C language Functions are available in the mathematics

library. How to use the functions in the

mathematics library?In the code: #include <math.h>Compile: gcc –lm f.c

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Outline




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Conversions and Casts

An arithmetic expression has both a value and a type Example:

int x=1, y=2;The type of expression (x+y) is int

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Arithmetic conversions Arithmetic conversions can occur when the

operands of a binary operator are evaluated.

Example:int i, float f;expression i+f

o i is promoted to a float o The expression i+f as a whole has type float.

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Arithmetic conversions Why type of an expression?

#include <math.h>main(){ int i=2; float f = 3.0; printf("%.2f\n", i+f); printf("%d\n", i+f);}

% gcc con.c% a.out5.001075052544%

The type of an expression The rules for conversions when types of the constants, variables and function calls making up the expression have different types.

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The integral promotions A char or short, either signed or unsigned,

can be used in any expression where an int or unsigned int may be used.

If all the values of the original type can be represented by an int, the value is converted to an int;

Otherwise it is converted to an unsigned int.

(unsigned) char, (unsigned) short int, unsigned int

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The usual arithmetic conversions If either operand is of type long double,

the other operand is converted to long double.

Otherwise, if either operand is of type double,the other operand is converted to double.

Otherwise, if either operand is of type float,the other operand is converted to float.float double long double

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Conversions and CastsThe usual arithmetic conversions (cont’d) Otherwise, all operands are of integral types

If either is of type unsigned long, the other unsigned long.

Otherwise if either long, the other unsigned,If a long can represent all the values of an

unsigned, then unsigned long.Otherwise, both unsigned long

Otherwise if either has type long, the other long

Otherwise if either has type unsigned, the other unsigned

Otherwise, both have type intshort int unsigned long unsigned long

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Cast operator: explicit conversions (type)

Example: int i(double) iCasts the value of i so the expression has

type doubleThe variable i itself remains unchanged.

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More Examples: (long)(‘A’+1.0) X=(float)((int)y+1) (double)(x=7)

But not (double) x=7

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Cast operator: unary operator The same precedence as other unary

operator Right-to-left associativity Example:

(float) i + 3 ((float) i) +3

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Summary An arithmetic expression has both a value

and a type Arithmetic conversions can occur when the

operands of a binary operator are evaluated.

Cast operator: explicit conversions(type)

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Outline




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End of Chapter 6: The Fundamental Data Type

Read 6.1 – 6.13

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Review of Chapter 3

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How true and false are implemented in C Representation of true and false

false: represented by any zero valueo int 0o floating 0.0o Null character ‘\0’o Null Pointer ( will be introduced in Chapter

8)

true: represented by any nonzero value

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Relational, Equality, and Logical Operators

Relational Operators: < > <= >=Equality Operators: == !=Logical Operators: ! && ||conditional operator: expr1? expr2: expr3

Semantics:First, expr1 is evaluated. If it is nonzero (true), then expr2 is evaluated, and

this is the value of the conditional expression as a whole.

If expr1 is zero (false), then expr3 is evaluated, and this is the value of the conditional expression as a whole.

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The if and if-else Statement

exp is enclosed by parentheses Where appropriate, compound statements

should be used to group a series of statements under the control of a single if expression

An if or if-else statement can be used as the statement part of another if or if-else statement.an else attaches to the nearest if.

if (expr) statement1

elsestatement2

if (expr) statement1

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The switch Statement

General form:

switch ( switch_exp ){ case constant_exp1: statements;

break; // optional case constant_exp2 : statements;

break; // optional ... case constant_expn: statements;

break; // optional default:

statements; break;

}

//optional

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The effect of a switch: Evaluate the switch_exp. Go to the case label having a constant value

that matches the value of the switch_exp.If a match is not found, go to the default

label. If there is no default label, terminate the

switch. Terminate the switch when a break

statement is encountered, or by “falling off the end”.

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break; // optional case constant_exp2 : statements; case constant_exp3 : statements; …../* no break */case constant_expi : statements;

break;……case constant_expn: statements;

break; // optional ……}Next statement;

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break; // optional ……case constant_expi : statements;


break; // optional default:

statements; break;

}Next statement;

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break; // optional ……case constant_expi : statements;


break; // optional }Next statement;

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The while Statement

General formwhile (expr)

StatementNext statement

First expr is evaluated. If expr is nonzero (true), then statement is

executed and control is passed back to the beginning of the while loop. Statement is repeatedly until expr is zero

(false) Then control passes to next statement.

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The for Statement

Semantics: First expr1 is evaluated. Then expr2 is evaluated.

If expr2 is nonzero (true), o then statement is executed,o expr3 is evaluatedo control passes back to the beginning of the for

loop again, except that evaluation of expr1 is skipped.

The process continues until expr2 is zero (false), at which point control passes to next statement.

for(expr1; expr2; expr3){

statement

} next statement

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The for Statement

for (expr1; expr2; expr3) Any of all of the expressions in a for statement

can be missing, but the two semicolons must remain.If expr1 is missing, no initialization step is

performed as part of the for loopWhen expr2 is mission, the rule is that the

test is always true.

for (expr1; expr2; expr3)statement

Next statement

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The do Statement

Semantics First statement is executed, and expr is

evaluated. If the value of expr is nonzero (true),

then control passes back to the beginning of the do statement, and process repeats itself.

When expr is zero (false), then control passes to next statement

do

statementwhile (expr);Next statement

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The Break and Continue Statements

break statement An exit from the innermost enclosing

loop (such as a while loop) statement or switch statement

continue statement Causes the current iteration of a loop to

stop and the next iteration to begin immediately.

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Review of Chapter 4

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Outline of Chapter 4

How to write a function? Function Invocation Function Definition The return Statement Function Prototypes

More about function Program Correctness: The assert() Macro Function Declarations from the Compiler’s Viewpoint Invocation and Call-by-Value Developing a Large Problem

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How to write a function?

#include <stdio.h>void prn_message(void);void prn_message(void);int main(void){ prn_message();prn_message(); printf(“Back to main function\n”); return 0;}void prn_message(void)void prn_message(void){{ printf(“A message for you: “);printf(“A message for you: “); printf(“Have a nice day!\n”);printf(“Have a nice day!\n”); return;return;}}

How to give the compiler information about the function?

Function prototype:How to pass control to the function?

Function InvocationHow to specify the function?

Function DefinitionHow to get the control back?

return statement

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How to write a function?Preprocessing directivesfunction prototype of fucntion1function prototype of fucntion2int main(void){ Body of function definition}Header of function1 definition{

Body of function definition}Header of function2 definition{

Body of function definition}

function invocations

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Program Correctness: The assert() Macro

C provides the assert() macro in assert.h to guarantee certain conditions assert(exp)

ensures the value of exp is trueif exp is false, the system prints out a

message and abort the program.

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Function Declarations from the Compiler’s Viewpoint

Preprocessing directivesfunction prototype of fucntion 1function prototype of fucntion 1int main(void){ Body of function definition}Header of function1 definition{


Body of function definition}

Preprocessing directivesHeader of function1 definition{


Body of function definition}int main(void){ Body of function definition}

Give either the function definition or the function prototype or both before a function is used

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Invocation and Call-by-Value

Function Invocation

fun_name(exp1, exp2); All arguments are passed call-by-value

Each argument is evaluated, and its value is used locally in place of the corresponding formal parameter.

If a variable is passed to a function, the stored value of that variable in the calling environment is not changed.

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#include <stdio.h>int min2(int a, int b);int min3(int a, int b, int c);

min.h

#include “min.h”int main(void){ printf("%d\n", min3(1,3,4) ); return 0;}

main.c

int min2(int a, int b){ if (a<b) return a; else return b;}int min3(int a, int b, int c){ int mofab = min2(a,b); return min2(mofab, c);}

min.c

f.h: function prototypesf1.c, f2.c, f3.c

function definitions

in each .c file#include “f.h”

gcc f1.c f2.c f3.c

gcc main.c min.c

Developing a Large Problem

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