Data Type, expression & flow of Control

2011-9-16 　胡俊峰

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C 语言的数据类型 C 语言的表达式 关系运算与关系表达式、逻辑运算与逻辑

表达式 C 语言的标准输入输出 条件与分支结构 循环控制

C 语言的数据类型 整数、浮点数编码 整数、浮点数运算 字符类型 溢出与精度问题 变量、常量及数组的使用

5

Integer Data Types (continued)

6

Data types (integer type)

Data typesize

（ bit ） range of values

short int   16-32K ~ 32K-1(- 32768 ~ 32767)

int 32 -2G ~ 2G-1

Unsigned short 16 64K -1 ~ 0

unsigned  32 4G-1 ~ 0

Character Data Type

ASCII character set (A-Za-z0-9, etc.)

stored in binary number format

uses char keyword

char is a single byte in size

also used for small integers

Floating Point Data Types

real numbers with a decimal and/or exponent (1.5 or 2.67e-3)

stored in floating point format (mantissa, exponent and sign bit)

single precision uses float keyword double precision uses double keyword long modifier can be applied to double

10

Floating-Point Data Types (cont.)

float literal is indicated by appending an f or F long double is created by appending an l or L

9.234 indicates a double literal9.234f indicates a float literal9.234L indicates a long double literal

11

Floating –point encoding Floating-point numbers consist of an ``exp

onent,'' ``significand'', and ``sign bit''

sign bit 1 sign bit 1 Exponent 7 significand 23

Over flow

Truncation error

C Constants

representation of a number, character or group of characters (i.e. a string)

a constant has a value and a type

integer, floating point, character, string

Integer Constants

hexadecimal, starts with 0x, digits are 0 – 9, a - f (e.g. 0x5e, 0xFF, 0X1234)

octal, starts with 0, digits are 0 - 7 (e.g. 017)

decimal, digits are 0 – 9 (e.g. 200, 7, 32767)

can have u (unsigned) or l (long) modifier suffix

Floating Point Constants

use decimal and/or exponential notation, digits are 0 – 9 with e and + or - (e.g. 1.5, 6.22e-2, 3e1, 2e+9)

single precision, uses f suffix (e.g. 1.5f)

double precision, default case (e.g. 1.5)

long double, uses L suffix (e.g. 1.5L)

Character Constants

enclosed in single quotes (e.g. ‘a’)

ASCII encoding

alphanumerics (e.g. ‘A’, ‘7’) and special characters (e.g. ‘$’, ‘%’)

escape sequences (e.g. ‘\n’, ‘\r’, ‘\\’) or in octal notation (e.g. ‘\377’, ‘\0’)

String Constants

contiguous group of characters

enclosed in double quotes (e.g. “how did I get here?”)

null terminated (‘\0’ char is at the end)

Variables

have a name, type and value

type name; (e.g. int sum;)

type name = initial_value; (e.g. int sum = 0;)

type name1, name2; (e.g. int sum1, sum2;)

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data type variableName1 [, variableName2];

int         i, j = 90; short    si; char         c1 = 'a';     float       balance, profit, loss;

Variable declaration :

Const of char

Const of integer

initialization

22

Declaration Statements (cont.)

C 语言的表达式 Statements and expression 算术表达式与算符的优先级 类型转换问题

C Expressions

constants, variables, functions calls and combinations of these (almost everything!)

evaluate to a type and value

examples: x, x + y, (x + y * z), sum = x + y

C Statements an expression followed by a semicolon ( ; )

{ } – compound statement or block; the only statement not requiring a terminating ;

( ) required around control expression of a conditional or iterative statement (e.g. if statement)

C Operators

assignment (=) and arithmetic operators (+ - * / %)

precedence, which operation is done first

associatively, how operations group when there is equal precedence

use parentheses ( ) for more control of the grouping

Assignment Operator

assignment = (a = 2)

the value of the “object” on the left side is replaced by the value of the expression on the right side

an “object” is a manipulatable region of storage (i.e. you are allowed to update its value)

the left side must be an “lvalue”, an expression which evaluates to an object (e.g. a variable)

has low precedence and associates right-to-left

Arithmetic Operators ： Binary

addition + (a + b)

subtraction - (a - b)

multiplication * (a * b)

division / (a / b)

modulus % (a % b)

* / % have higher precedence than + - and all associate left-to-right

Arithmetic Operators ： Unary

plus + (+ a) equivalent to (0 + a)

minus - (- a) equivalent to (0 – a)

higher precedence than binary arithmetic operators

associate right-to-left

Precedence of Operators

defines which operators take effect first

consult the operator precedence table

a * b + c is equivalent to (a * b) + c instead of a * (b + c)

Associativity of Operators

defines how operations group when the operators have equal precedence

consult the operator precedence table

a - b + c is equivalent to (a - b) + c instead of a - (b + c)

Grouping Parentheses

can use parentheses ( ) to force the order of evaluation

a * (b + c) instead of a * b + c

a – (b + c) instead of a – b + c

Conversions arithmetic expressions with the same or different dat

a type operands

if the same data type, the operations will be performed in that type

if different data types, the smaller type is usually converted to the bigger type before the operations are performed

f1 = 2 / 100 vs f1 = 2 / 100.0

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Mixed-mode expression (automatic type conversion)

关系运算与关系表达式、逻辑运算与逻辑表达式 关系运算、关系表达式 逻辑运算、逻辑表达式 算术运算的逻辑含义与各种运算的优先级

Relational Expressions

integer (char)floatdouble

Same Type

0 falsenot 0 true

Relational Expressions (cont.)

Can accept data which can be arranged in ordering sequence

Relational Expressions (cont.) Characters behave the same way as an integer

in a relational expression

Relational Expressions (cont.) —— evaluate and then compare have lower precedence

Logical Operations

Can take in operands that evaluated as true (1) or false (0)

Use && (and), || (or), ! (not) to build more complex conditional expressions.

Logical expression is another kind of conditional expression and can also be used directly in selection

Truth table of && (and)

R1 && R2 0 1

0 0 0

1 0 1

Truth table of || (or)

b1 || b2 0 1

0 0 1

1 1 1

Logical Operation ! (NOT)

Precedence of operators

You can always use parenthesis to change the precedence of operators

Relational operation

logical operation

Logical expressions —— conditional expressions

Can take in any valid expression as operands

0 is interpreted as False

None 0 is interpreted as True

int i = 15, j = 30;

double a = 12.0, b = 2.0, complete = 0.0;

Logical expressions —— short-circuit evaluation

a || b a && b

2 || a > b 0 && a == b

Logic operations

1bit 1bit

C1 && C2

||

⊕ 1bit

Compound Relational Expressions relational expr logical oper relational expr

for example: (a > 12) && (a < 20)

for example: (c < 70) || (!valid)

year%4==0

year%100!=00

1

year%400==01

0

0

1

Is leap year: y%4 == 0 && (y%100 != 0 || y%400 == 0)

Input a year

10 1

0

y%100 != 0 y%100No zero trueZero false

C 语言的标准输入输出 标准输入输出原理 输入 \ 输出格式串中的占位符与转义字符 输入输出函数的返回值

printf()

formatted output to the console

printf(control string, variable argument list)

the control string can be simple text or can be embedded with conversion specifications (these begin with a % and end with a conversion character)

the variable argument list is a comma separated list of expressions, and each argument must correspond to one conversion specification in the control string

printf()

arg1 arg2 …

conversion Contral string: “%d;%f; %c”

arg3

5;12.000000;A

printf() Examples

printf(“This is simple text for output”)

printf(“My bowling average is %d”, average)

printf(“The date is %i %i %i”, 2, 5, 2003)

printf(“The answer is %f”, somefloatvalue)

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Displaying Numerical Values (cont.)

printf(“conversion control sequence” ， argument list)

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Displaying Numerical Values(cont.)

Invoking or calling the printf() functiondisplay as an integer

Escape sequence

printf() Conversion Characters

d or i – integer in decimal

o – integer in octal

x – integer in hexadecimal

e, f, g – floating point

c – single character

s – character string

The scanf() function formatted input from the console

scanf(control string, variable argument address list)

the control string can be simple text or can be embedded with conversion specifications (these begin with a % and end with a conversion character)

the variable argument list is a comma separated list of argument address, and each argument address must correspond to one conversion specification in the control string

scanf()

arg1 arg2 …

conversion Contral string: “%d;%f; %c”

arg3

5 12.000000 A

scanf() function

条件与分支结构 程序分支与语句块 statement block, compound statement 条件语句的组合与嵌套 Switch 语句与条件表达式

Selection

selection is a single-entry/single-exit structure: execute only when condition is satisfied.

true

falseRelationa

lexpressio

n

printf( “Passed”);

S >= 60

if statement

single selection

uses the if keyword

controlled by a test expression, typically a relational expression, which must be enclosed in parentheses ( )

select a single statement or a compound statement (i.e. a block)

the statement is selected if the test expression is true

if (grade >= 60){ printf(“passed”); credit += 2; }

false

true

grade >= 60

printf(“passed”); credit += 2;

Compound statement: statements enclosed with brackets.

The if-else Statement

if (expression)

statement1;

else

statement2; If the value of expression is 0 the statement

after the reserved word else, statement2, is executed

Exp ： #include <stdio.h>

int main (){    int score;    printf("Please input your score:");    scanf("%d",&score);    if (score>=60){       printf("Passed!\n");    }    else

       printf("Sorry you failed!\n");    return 0;}

The if-else Chain Nested if statement:

if (expression1) statement1;else if (expression2) statement2; else statement3;

The if/else Selection Structure

If student’s grade is greater than or equal to 90Print “A”

else If student’s grade is greater than or equal to 80 Print “B”else If student’s grade is greater than or equal to

70 Print “C” else If student’s grade is greater than or equal

to 60 Print “D” else Print “F”

if .. else if chain else if

if

exp1

exp3

exp2else if 1

1

1

0

case1 case2 case3 case4

The switch Statement

Terminated with a colon

default is optional

If the break statement was omitted, the following case would be executed

switch (exp)

case v1:

case v2:

statements

statements

statements

statements

statements

case v3:

case v4:

case v5:

default:

Case study:

Conditional Operator ? : (a ? b : c)

has three operands

use as shorthand for a simple if else

conditional operator has low precedence and associates right-to-left

Conditional Expression

test expression ? value if true : value if false

for example: (flag != 0) ? “true” : “false”

useful for string output and simple assignment

Conditional Expression// show conditional expression ? :

string = (flag != 0) ? “true” : “false” ;

// same as the following if else

if (flag != 0){ string = “true”;}else{ string = “false”;}

循环控制 循环变量与循环体 循环方式与结束条件 多重循环与算法

Repetition Statements

repeat statement(s) a controlled number of times; can be infinite

controlled by a test expression, typically a relational expression, which must be enclosed in parentheses ( )

control a single statement or a compound statement (i.e. a block)

Repetition Statements (cont.)

for statement

good for counter-controlled or indexed loops

uses for keyword

index variable or loop counter (typically an integer variable), controls the loop

condition is tested at the top of the loop (i.e. before executing the loop statements)

has initialization and update expressions for manipulating the loop counter

initializing;

testing;

altering

C Array — 0 based

while statement

good for flag or sentinel value conditions

uses while keyword

condition is tested at the top of the loop (i.e. before executing the loop statements)

while statement (cont.)

do while statement

good for flag or sentinel value conditions, when you need to execute the loop statements at least once

uses do and while keywords (as a pair)

condition is tested at the bottom of the loop (i.e. after executing the loop statements)

requires a semicolon ; at the end

Enter at least once, often used in verification

break and continue statements

break statement, used for early termination of a loop

continue statement, used for early continuation of a loop

break;

continue;

Nested loop

#define NUM 4 int i;j; for ( i = NUM; i > 0; i--) { for ( j = 0; j<i; j++) printf(“*”); printf(“\n”); }

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