C程序设计语言

高级语言的含义：what to do , how to do

二元一次方程： ax2+bx+c=0

手工求解法：1)a=0 1.1)b=0 1.1.1)c=0 任意数

1.1.2)c<>0 无解

1.2)b<>0 x=-(c/b)

2) a<>0 x1=(-b+sqrt(b2-4a*c))/(2*a)

x2=(-b-sqrt(b2-4a*c))/(2*a)

计算机求解法：输入a b c的值，通过计算输出x解的结果

1)a、b、c为任意值，由键盘输入

2)分析判断：算法部分

3)输出：x的结果解

4)算法语句书写规则：数据类型、运算符、表达式、函数

Chapter 1: Types, Operators, and Expressions

类型、运算符和表达式

§2.1 Variable Names (变量名，概念)

·letters (include “_”) and digitals, begin with letter

·upper case and lower case letters are DISTINCT

·keywords like if, else, int, float, etc.,are reserved

Legal variable names (or identifier):

sum, average, class, day, month, student_name, _above,

lotus_1_2_3, basic, The_C_Programming_Language

Illegal variable names:

M.D.Join, $123, #33, 3D64, a>b

§2.2 Data Types and Sizes (数据类型和大小)

☆Basic data types in C:

·char a single byte, holding ONE character (1 byte)

·int an integer (2 or 4 bytes)

·float single-precision floating point (4 bytes)

·double double-precision floating point (8 bytes)

所有的基本类型都是“数值类型”，其数据都可参与数值运算。

☆Some qualifiers can be applied to these basic types:

·short and long apply to integers:

short int sh or short sh (int can be omitted)

long int counter or long counter

·signed or unsigned may be applied to char or ANY integer

signed can ALWAYS be omitted

signed char (or char) values between -128~127 unsigned char values between 0~255

signed int (or int) values between -2n-1~2n-1-1

unsigned int values between 0~2n-1

☆function sizeof return the size of the type or variable.

char ch;

sizeof(char) = 1 or sizeof(ch) = 1 (byte)

§2.3 Constants (常量)

☆int constant

·int: 123, -456

·long: 123456789l or 123456789L

·unsigned int: 123u or 123U

·unsigned long: 123456789ul or 123456789UL

·octal(八进制): A leading 0 on an integer constant

e.g. 037 (= 31 in decimal)

·Hexadecimal(十六进制): A leading 0x or 0X on an int constant

e.g. 0x1f or 0X1F (= 31 in decimal)

☆float or double constant

·float or double: 123.4 or 1e-2

·float ONLY: 123.4f or 123.4F

☆char constant: ‘x’, ‘0’, ‘\n’, ‘\013’, ‘\xb’, ‘\x7’

·The complete set of escape sequences:

\a alert(bell) character \\ backslash

\b backspace \? question mark

\f formfeed \’ single quote

\n newline \” double quote

\r carriage return \ooo octal number

\t horizontal tab \xhh hex number

\v vertical tab

·’\0’ represents null character, with value zero.

☆string constant:

·“I am a string” I a m a s t r i n g\0

·“” null string \0

·function strlen(s) return the length of its character string argument s, excluding the terminal ‘\0’.

/* strlen: return length of s */

int strlen(char s[])

{

int i;

i = 0;

while (s[i] != 0)

i++;

return(i);

}

☆the difference between ‘x’ and “x”:

·‘x’ is a integer, used to produce the numeric value of the letter x in the machine’s character set(always ASCII-120).

x

·“x” is an array of characters that contains one character (the letter x) and a ‘\0’.

x \0

☆symbolic constant(符号常量)

#define  BELL ‘\007’ /* ASCII bell character */

#define PRICE 30

☆enumeration constant(枚举常量):

·enum boolean {NO, YES}; /* No = 0, and YES = 1 */

·enum escapes {BELL = ‘\a’, BACKSPACE = ‘\b’, TAB = ‘\t’,

NEWLINE = ‘\n’, VTAB = ‘\v’, RETURN = ‘\r’};

·enum months {JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG,

SEP,OCT,NOV,DEC}; /*FEB is 2, MAR is 3, etc.*/

§2.4 Declarations (变量定义)

☆All variables MUST be declared before use. 先定义，后使用

☆ Declaration form: type var1, var2, …, varN;

int lower, upper, step;

char c, line[1000];

Could equally well be written as

int  lower;

int upper;

int step;

char c;

char line[1000];

☆ A variable may also be initialized in its declaration.

·general form:

char esc = ‘\\’;

int i = 0, j, k=1, m;

int  limit = MAXLINE+1;

float eps = 1.0e-5;

·const form: specify that the value will not be changed.

const double pi = 3.1415926535;

const char message[] = “warning:”;

§2.5 Arithmetic Operators (算术运算符)

·binary arithmetic operators: +, -, *, /, %(modulus op.) .

·+, -, *, and / can be applied to any basic type, but %

can’t be applied to float and double.

·ATTENTION(注意)!!!

float(double)/float(double) => float(double)

float(double)/int => float(double)

int/float(double) => float(double)

int/int => int

e.g. 10.0/4 = 2.5, but 10/4 = 2 -10/4 = -2

·10%3 = 1 -10%3 = -1 10 % 2 = 0

N = (N/m)*m + N%m where, N and m are both int.

·Precedence & associativity(优先级和结合性):

“*” = “/” = “%” > “+” = “-”

All arithmetic operators associate left to right.

e.g. 3 + 5 * 2 - 10 / 4 % 3  <=> 3 + (5 * 2) - 10 / 4 % 3

=> 3 + 10 - 10 / 4 % 3 <=> (3 + 10) - 10 / 4 % 3

=> 13 - 10 / 4 % 3 <=> 13 - (10 / 4) % 3

=> 13 - 2 % 3 <=> 13 - (2%3)

=> 13 - 2 <=> (13 - 2)

=> 11 <=> 11

·Arithmetic expression_r(算术表达式):

用算术运算符和括号将运算对象(操作数)连接起来的、符合C语法规则的式子，称算术表达式。运算对象包括常量、变量、函数等。e.g.:

a * b / c - 1.5 + ‘a’

运算的结果即为算术表达式的值。

§2.6 Assignment Operators and Expressions赋值运算符和表达式

·Assignment operator: “=”

e.g.: x = 12 “=” 号左边必须是一个变量！

·Compound assignment operators(复合的赋值运算符): op=

where, op is one of

+, -, *, /, %, <>, &, ^, |

expr1 op= expr2 <==> expr1 = (expr1) op (expr2)

where, expr1 must be a variable.

e.g.:

a += 3 <==> a = a + 3

x *= y+8 <==> x = x * (y+8)

x %= 3 <==> x = x % 3

·由赋值运算符将一个变量和一个表达式连接起来的式子称为“赋值表达式”。

(此“表达式”也可以是一个赋值表达式)

·赋值表达式的值就是被赋值的变量的值。

·赋值运算符的按照“自右向左”的结合顺序。

e.g.: a = 3 表达式的值 => 3

a = (b = 5) <==> a = b = 5 => 5

a = b = c = 5 => 5

a = 5 + (c=6) => 11

a = (b=4) + (c=6) => 10

a = (b=10) / (c=2) => 5

a += a -= a*a <==> a += (a -= (a*a))

如果a的初始值为12， 则

(1) 先算a*a = 12*12 = 144, 此时a = 12

(2) 再算a -= 144， 即 a=a-144=12-144=-132, 此时，a = -132

(3) 然后算 a += -132, 即 a = a+(-132)=(-132)+(-132)=-264