c++学习笔记（4）

1. 一维数组和C字符串：数字是用来存储相同类型变量的数据集合

c++要求在声明数组时，数组的大小是常量：

int size=4;

double numbers[size];        // wrong

const int size=4;

double numbers[size];      // correct

2. 数组初始化语句

double number[] = {1.1, 3, 4, 9.6}

必须在一条语句内完成声明和初始化

注 c++ 中数组复制，需要在两个数组之间逐个元素进行复制：

for(int i=0; i<size; i++)

{

    a[i] = b[i];

}

3.实现数组reshuffle

方法：对于数组元素numbers[i], 随机产生一个下标 j (0 <= j <= i ), 交换 numbers[i] 和 numbers[j] 的顺序：

#include <iostream>
#include <cstdlib>
#include <time.h>
 
using namespace std;
const int SIZE=10;
int main(int argc, char *argv[])
{
	srand(time(0));
	int numbers[SIZE] = {0,1,2,3,4,5,6,7,8,9};  // 实现数组reshuffle
    for(int i=SIZE-1; i>0; i--)
    {
    	int j = rand()%(i+1);   // generator a random number between 0~i
    	int tmp = numbers[i];
    	numbers[i] = numbers[j];
    	numbers[j] = tmp;
    }
    for(int i=0; i<SIZE; i++)
    {
    	cout << numbers[i] << " ";
    }
    cout << endl;
    return 0;
}

string month[ ] = {"January" , " Feburary", ......., "December"}

5. 一副纸牌

思路： 数组实现

int cards[52];

分组： 0-12 ， 13-25， 26-38， 39-51   （spade, heart, diamond, club）

使用string suit[ ] ={"spade", ......}

代码：

#include <iostream>
#include <ctime>
#include <string>
 
using namespace std;
 
const int SIZE = 52;   // number of cards;
int main(int argc, char *argv[])
{
	srand(time(0));
	int cards[SIZE];
	string suits[] = {"spade", "heart", "diamond", "club"};
	string ranks[] = {"Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"};
	// 复初值
	for(int i=0; i<SIZE; i++)
	{
		cards[i] = i;
	} 
	for(int i=SIZE-1; i>0; i--) // reshuffle
	{
		int j= rand() % (i+1);   // generate a random index between 0 and i
		int tmp = cards[i];
		cards[i] = cards[j];
		cards[j] = tmp;
	}
	
	for(int i=0; i<SIZE; i++)
	{
		cout << cards[i] << " ";
		if(i%10 == 0)   
		     cout << endl;
	}
	cout << endl;
	
	for(int i=0; i<4; i++)
	{
	   string suit = suits[cards[i]/13];
	   string rank = ranks[cards[i]%13];
	   cout << "The selected card is " << suit << " " << rank << endl; 
	}
	
	return 0;
}

运行结果：

4.数组作为函数参数

当一个数组参数传递给函数，数组的起始地址被传递给了函数中的数组参数。实际参数和形式参数使用的是同一个数组。

5.防止函数修改传递参数的数组：可以将数组参数声明为const类型的数组

6. 数组作为函数的返回值

c++不允许直接返回数组，可以向函数传递两个数组

void reverse(int numbers[ ],   int  newNumbers[ ] ,  int SIZE)

{

       ..............

}

数组逆序实现：

#include <iostream>
#include <ctime>
#include <string>
 
using namespace std;
 
void printList(int numbers[], int size)
{
	for(int i=0; i<size; i++)
	{
		cout << numbers[i] << " ";
	}
	cout << endl;
}
 
void reverseList(const int numbers[], int newList[], int size)
{
	for(int i=0; i<size; i++)
	{
		newList[size-1-i] = numbers[i];
	}
}
 
int main(int argc, char *argv[])
{
    int num[5] = {1, 2, 3, 4, 5};
    int newlist[5];
    reverseList(num, newlist, 5);
    printList(newlist, 5);	
    return 0;
}

另一种实现：

#include <iostream>
#include <ctime>
#include <string>
 
using namespace std;
 
// 这种方式只用传递一个数组作为参数，但是原数组会被改变 
void reverseList(int numbers[], int size)    
{
	for(int i=0; i<size/2; i++)
	{
		int tmp = numbers[i];
		numbers[i] = numbers[size-1-i];
		numbers[size-1-i] = tmp;
	}
}
 
void printList(int numbers[], int size)
{
	for(int i=0; i<size; i++)
	{
		cout << numbers[i] << " ";
	}
	cout << endl;
}
 
int main(int argc, char *argv[])
{
    int num[5] = {1, 2, 3, 4, 5};
    reverseList(num, 5);
    printList(num, 5);
    return 0;
}

搜索数组：顺序搜索和二分搜索

#include <iostream>
#include <ctime>
#include <string>
#include <iomanip>
#include <cstdlib>
 
using namespace std;
 
int binarySearch(int [], int, int);
 
int main(int argc, char *argv[])
{
	int test[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
	int tmp = binarySearch(test, 10, 6);
	if(tmp==-1)
	{
		cout << "Not Found" << endl;
	}	
	else
	{
		cout << "The index is " << tmp << endl;
	}
	
	return 0;
}
 
 
int binarySearch(int list[], int listSize, int key)
{
	int low = 0;
	int high = listSize - 1;
	int mid = listSize / 2;
	while(low <= high)
	{
	   if(key<list[mid])  
	        high = mid - 1;
	   else if(key>list[mid])   
	        low = mid + 1;
	   else 
	        return mid;
	   mid = (low + high) / 2;	
	}
	return -1;
}
 
 

数组排序+二分还查找+逆序排列：

#include <iostream>
#include <ctime>
#include <string>
#include <iomanip>
#include <cstdlib>
 
using namespace std;
 
int binarySearch(int [], int, int);
void select_sorted(int [], int);  //选择排序 
void printList(int [], int);
void reverseList(int [], int);
 
int main(int argc, char *argv[])
{
	int test[10];
	cout << "Enter ten numbers: " << endl;
	for(int i=0; i<10; i++)
	{
		cout << "Enter: ";
		cin >> test[i];
	}
	cout << "Yuo Enter a list: " << endl;
	printList(test, 10);
	select_sorted(test, 10);    // 对数组进行排序
	cout << "The list after sorted is: " << endl;
	printList(test, 10);
	reverseList(test, 10);
	cout << "The list after reverse: " << endl;
	printList(test, 10);
	cout << "Enter the number you want to find: ";
	int num;
	cin >> num;
	int index = binarySearch(test, 10, num);
	if(index == -1)
	{
		cout << "Not found in the list!" << endl;
	} 
	else
	{
		cout << "The index is " << index << endl;
	}
	 
	return 0;
}
 
 
 
int binarySearch(int list[], int listSize, int key)
{
	int low = 0;
	int high = listSize - 1;
	int mid = listSize / 2;
	while(low <= high)
	{
	   if(key<list[mid])  
	        high = mid - 1;
	   else if(key>list[mid])   
	        low = mid + 1;
	   else 
	        return mid;
	   mid = (low + high) / 2;	
	}
	return -1;
}
 
// 函数重载
//double binarySearch(double list[], int listSize, double key) 
 
void select_sorted(int list[], int listSize)
{
	/* 选择排序*/ 
	//int min_number = list[0];     写到这里你是错误的 
	//int min_number_index = 0;
	for(int i=0; i<listSize-1; i++)
	{
	   int min_number = list[i];
	   int min_number_index = i;
	   
	   for(int j=i; j<listSize; j++)
       {
       	    if(min_number > list[j])
	       {
	            min_number = list[j];
	            min_number_index = j;				
	       }
       }
       
       int tmp = list[i];
       list[i] = list[min_number_index];
       list[min_number_index] = tmp; 
	}
} 
 
void reverseList(int list[], int size)
{
    for(int i=0; i<size/2; i++)
	{
		int tmp = list[i];
		list[i] = list[size-i-1];
		list[size-i-1] = tmp;
	}	
} 
 
void printList(int list[], int size)
{
	for(int i=0; i<size; i++)
	{
		cout << list[i] << "  ";
	}
	cout << endl;
}
 
 

C字符串函数s

<cstring> 中的函数

strlen()

strcpy()

strncpy()

strcat()

strncat()

strcmp()

strncmp()

cstdlib()中的函数

int  atoi()     返回字符串对应的int值

float  atof()

double  atol()

itoa（）将数子转化为字符串

6.  字符串和数字之间的转化

#include <iostream>
#include <ctime>
#include <string>
#include <iomanip>
#include <cstdlib>
 
using namespace std;
 
 
int main(int argc, char *argv[])
{
	// 使用atoi将字符串转化为int
	char s1[] = "250";
	char s2[] = "100";
	int num = atoi(s1) + atoi(s2);
	cout << "The number is " << num << endl;
	
	char s3[] = "20.78";
	char s4[] = "90.33";
	
	double num1 = atof(s3) + atof(s4);
	cout << "THE number is " << num1 << endl;
   // 使用itoa()函数将整数转化为字符串：
   char ss1[15];
   char ss2[15];
   char ss3[15];
   
   itoa(100, ss1, 16);   // 将100按16进制转化为字符串存到ss1中 
   itoa(100, ss2, 2);
   itoa(100, ss3, 10);
   
   cout << "The hex for 100 is " << ss1 << endl;
   cout << "The binary for 100 is " << ss2 << endl;
   cout << "The decimal for 100 is " << ss3 << endl;
    
	return 0;
}