21T2 9024-Week 01

printf

Loops

Functions

Data Types

Aggregate Data Types

Arrays

scanf and atoi

Arrays and Functions

Multi-dimensional Arrays

Defining New Data Types

Structures

Abstract Data Types 抽象数据类型

Stack 堆栈，LIFO 后进先出

Compilers 编译器

Summary

CSE

gcc prog.c

ls -lt

./a.out

gcc -Wall prog.c // show all warnings

gcc -o gcd prog.c //give a.out a new name

printf

printf(format-string, expr...);

format-string

%d decimal

%f floating-point

%c character

%s string

\n new line

\" quotation mark

printf("%8.3f\n", 3.14159)

3.142

for k = 6

k++;//k=k+1

n=k--; //assign k to n, then decrement k by 1

// k=6 n=7

++k;///increment k by 1, afterwards, k=7;

n=--k; // first drcrement k by 1, then assign k to n

//k=6 n=6

if()
{statements;
}if()
{statements 1;
}
else
{statements 2;
}

Conditionals

int main()
{int x,y;if((x>y) && !(y-x <= 0)) //前为真则后不为真/前假后真{printf("Aye\n");}else{printf("Nay\n"); // final result}
}

int main()
{int x;x= (x >= 0) + (x < 0);printf("%d\n",x);
}// always 1. true-printf 1, false 0, always 0+1 or 1+0

Loops

while loop /more common

while (expression){

statements;

}

do...while loop

do {

statements;

} while (expression); // at least do the loop once

for loop

for (expr1;expr2;expr3){

statements;

}

expr1 before loop starts

expr2 check if the loop can contine

expr3 how to caculate at thhe end of this loop

Exercise 4-output

int main()
{
int i, j;
for (i = 8; i > 1; i /= 2) {for (j = i; j >= 1; j--) {printf("%d%d\n", i, j);}printf("\n");
}
}

Functions

return-type function-name(parameters) {declarationsstatementsreturn …;
}

如果return_type为void，则函数不返回值

如果parameters为void，则函数没有参数

Fuctions always return something

return=函数最后输出

Data Types

char 'A'

int 2, -17

float 3.14159

double 3.14159265358979

Aggregate Data Types

all elements have same base type eg:char s[50]; int v[100]

combine different base types eg:struct student { char name[30]; int zID; }

Arrays

size N, valid subscripts are 0...N-1

Examples

int a[20];

char b[10];

我们可以在文件的顶部定义一个符号常量

#define SPEED_OF_LIGHT 299792458.0
#define ERROR_MESSAGE "Out of memory.\n"

C Coding Style Guide (http://wiki.cse.unsw.edu.au/info/CoreCourses/StyleGuide)

数组初始化

char s[6]   = {'h', 'e', 'l', 'l', 'o', '\0'};
char t[6]   = "hello";
int fib[20] = {1, 1};//fib[0]=fib[1]=1, fib[2]未定义
int vec[]   = {5, 4, 3, 2, 1};

Exercise #5-output

#include <stdio.h>
int main(void) {int arr[3] = {10,10,10};char str[] = "Art";// str[3]=A r t \0int i;for (i = 1; i < 3; i++) {arr[i] = arr[i-1] + arr[i] +1;str[i] = str[i+1];}printf("Array[2] = %d\n", arr[2]);printf("String = \"%s\"\n", str);return 0;}//Array[2] = 32 String = "At"

scanf and atoi

从标准输入读取的格式化输入（如键盘）

scanf(format-string, expr1, expr2, …);

将字符串转换为整数

int value = atoi(string);

#include <stdio.h>   // includes definition of BUFSIZ (usually =512) and scanf()
#include <stdlib.h>  // includes definition of atoi()...char str[BUFSIZ];
int n;printf("Enter a string: ");
scanf("%s", str);
n = atoi(str);
printf("You entered: \"%s\". This converts to integer %d.\n", str, n);

result
Enter a string: 9024
You entered: "9024". This converts to integer 9024.

Arrays and Functions

当数组作为参数传递给函数时,实际传递的是数组开头的地址

函数中数组的字符类型已知，大小未知

int total, vec[20];
…
total = sum(vec);

因为函数不知道数组有多大，所以可以将数组的大小作为一个额外参数传入，或者包含一个“终止值”来标记数组的结束。

int total, vec[20];
…
total = sum(vec,20);

Exercise #6 实现对数组中所有元素求和的函数，使用 int sum(int[],int)

int sum(int vec[], int dim)
{int i, total = 0;for(i=0;i<dim;i++){total += vec[i];}return total;
}

Multi-dimensional Arrays

q[0][1]==2.7 r[1][3]==8 q[1]=={3.1,0.1}

Defining New Data Types

typedef float Real;//定义新数据类名称
Real complex_calculation(Real a, Real b)
{Real c = log(a+b);...//based on exist datatypereturn c;
}

Structures

是一组变量的集合，可能是不同类型的

typedef struct {char name[30];int  zID;
} StudentT;

结构体可以嵌套在另一个结构体中

typedef struct {int day, month;
} DateT;typedef struct {int hour, minute;
} TimeT;typedef struct {char   plate[7];   // e.g. "DSA42X"double speed;DateT  d;TimeT  t;
} TicketT;

---------------------------------
| D | S | A | 4 | 2 | X | \0|   |    7 bytes + 1 padding
---------------------------------
|                          68.4 |    8 bytes
---------------------------------
|             2 |             6 |    8 bytes
---------------------------------
|            20 |            45 |    8 bytes
---------------------------------

定义结构化数据类型本身不会分配任何内存

我们需要声明一个变量来分配内存

使用上述TicketT类型，我们声明并使用变量

#define NUM_TICKETS 1500typedef struct {…} TicketT;TicketT tickets[NUM_TICKETS];  // array of structs// Print all speeding tickets in a readable format
for (i = 0; i < NUM_TICKETS; i++) {printf("%s %6.2f %d/%d at %d:%d\n", tickets[i].plate,tickets[i].speed,tickets[i].d.day,tickets[i].d.month,tickets[i].t.hour,tickets[i].t.minute);
}// Sample output:
//
// DSA42X  68.40 2/6 at 20:45

%6.2f 6个字节来输出数字，取小数点后两位

结构体可以作为参数传递给函数：

void print_date(DateT d) {printf("%d/%d\n", d.day, d.month);
}int is_winter(DateT d) {return ( (d.month >= 6) && (d.month <= 8) );
}

Abstract Data Types 抽象数据类型

是一种信息隐藏方式

围绕数据建立分装

用户只能看到ADT的接口

ADT很重要，因为…

促进复杂程序的分解

使更改对客户端不可见

提高软件的可读性和结构化

允许在其他系统中重复使用模块

ADO=抽象数据对象

ADT=抽象数据类型

Stack 堆栈，LIFO 后进先出

创建空堆栈

把item插入（推）到堆栈上

删除（弹出）最近使用的item

检查堆栈是否为空

应用：在文本编辑器中撤消序列，括号匹配算法

Stack  Operation  Return value

? create -

-   isempty true

- push a -

a push b -

a b push c -

a b c pop   c

a b   isempty false

堆栈和队列（Stack vs Queue）

队列 FIFO 先进先出

Exercise #7- Stack&Queue

考虑前面的示例，但是使用队列而不是堆栈。哪个元素会首先被取出（“出列”）

Stack as ADO

// Stack ADO header file#define MAXITEMS 10void StackInit();      // set up empty stack
int  StackIsEmpty();   // check whether stack is empty
void StackPush(char);  // insert char on top of stack
char StackPop();       // remove char from top of stack

#include "Stack.h"
#include <assert.h>// define the Data Structure
typedef struct {char item[MAXITEMS];int  top;
} stackRep;// define the Data Object
static stackRep stackObject;// set up empty stack
void StackInit() {stackObject.top = -1;
}// check whether stack is empty
int StackIsEmpty() {return (stackObject.top < 0);
}
// insert char on top of stack
void StackPush(char ch) {assert(stackObject.top < MAXITEMS-1);stackObject.top++;int i = stackObject.top;stackObject.item[i] = ch;
}// remove char from top of stack
char StackPop() {assert(stackObject.top > -1);int i = stackObject.top;char ch = stackObject.item[i];stackObject.top--;return ch;
}//assert(test) terminates program with error message if test fails
//static Type Var declares Var as local to Stack.c

Exercise#8 Bracket Matching

括号匹配…检查所有的开始括号，如“（”、“[”、“{”是否有匹配的结束括号“）”、“]”、“}”

(a+b) * c
a[i]+b[j]*c[k])
(a[i]+b[j])*c[k]
a(a+b]*c
void f(char a[], int n) {int i; for(i=0;i<n;i++) { a[i] = (a[i]*a[i])*(i+1); }}
a(a+b * c

bracketMatching(s):
|  Input  stream s of characters
|  Output true if parentheses in s balanced, false otherwise
|
|  for each ch in s do
|  |  if ch = open bracket then
|  |     push ch onto stack
|  |  else if ch = closing bracket then
|  |  |  if stack is empty then
|  |  |     return false                    // opening bracket missing (case 1)
|  |  |  else
|  |  |     pop top of stack
|  |  |     if brackets do not match then
|  |  |        return false                 // wrong closing bracket (case 2)
|  |  |     end if
|  |  |  end if
|  |  end if
|  end for
|  if stack is not empty then return false  // some brackets unmatched (case 3)
|                        else return true

Compilers 编译器

Summary

Introduction to Algorithms and Data Structures
C programming language, compiling with gcc
- Basic data types (char, int, float)
- Basic programming constructs (if … else conditionals, while loops, for loops)
- Basic data structures (atomic data types, arrays, structures)
Introduction to ADTs
- Compilation
Suggested reading (Moffat):
- introduction to C … Ch. 1; Ch. 2.1-2.3, 2.5-2.6;
- conditionals and loops … Ch. 3.1-3.3; Ch. 4.1-4.4
- arrays … Ch. 7.1, 7.5-7.6
- structures … Ch. 8.1
Suggested reading (Sedgewick):
- introduction to ADTs … Ch. 4.1-4.3

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21T2 9024-Week 01

printf

Loops

Functions

Data Types

Aggregate Data Types

Arrays

scanf and atoi

Arrays and Functions

Multi-dimensional Arrays

Defining New Data Types

Structures

Abstract Data Types 抽象数据类型

Stack 堆栈，LIFO 后进先出

Compilers 编译器

Summary

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