题目：

电话的号码盘一般可以用于输入字母，如用2可以输入A，B，C，用3可以输入D，E，F等，对于号码5869872可以依次输出其代表的所有的字母组合。

解法一：直接循环法：

#include<iostream>
#include<stdio.h>

using namespace std;
#define TelLength 3

int main()
{
	char c[10][10]= 
	{
			"",  //0
			"",  //1
			"ABC", //2
			"DEF", //3
			"GHI", //4
			"JKL", //5
			"MNO", //6
			"PQRS", //7
			"TUV", //8
			"WXYZ" //9
	};
	int total[10] = {0,0,3,3,3,3,4,3,4};
	int number[TelLength] = {4,2,7};
	int answer[TelLength] = {0,0,0};

	cout << "427" << "对应的所有英文是：\n";

	for(answer[0] = 0; answer[0] < total[number[0]]; answer[0] ++)
		for(answer[1] = 0; answer[1] < total[number[1]]; answer[1] ++)
			for(answer[2] = 0; answer[2] < total[number[2]]; answer[2] ++)
			{
				for(int i = 0; i < TelLength; i ++)
					cout << c[number[i]][answer[i]];
				cout << "\n";
			}
	
	


	getchar();
	return 0;
}

以上代码是三级的循环，如果多四级或5级的呢，那再加循环，太麻烦了。

来看下面的一种解法。

#include<iostream>
#include<stdio.h>

using namespace std;
#define TelLength 3
int main()
{
	char c[10][10]= 
	{
			"",  //0
			"",  //1
			"ABC", //2
			"DEF", //3
			"GHI", //4
			"JKL", //5
			"MNO", //6
			"PQRS", //7
			"TUV", //8
			"WXYZ" //9
	};
	int total[10] = {0,0,3,3,3,3,4,3,4};
	int number[TelLength] = {4,2,7};
	int answer[TelLength] = {0,0,0};

	cout << "427" << "对应的所有英文是：\n";
	
	while(true)
	{
		for(int i = 0; i < TelLength; i ++)
			cout << c[number[i]][answer[i]];
		cout << "\n";
		int k = TelLength - 1;
		while(k >=0)
		{
			if(answer[k] < total[number[k]] - 1)
			{
				answer[k] ++;
				break;
			}
			else
			{
				answer[k] = 0; k --;
			}
		}
		if( k < 0)
			break;
	}
	getchar();
	return 0;
}


void RecursiveSearch(char c[10][10], int total[10], int* number, int* answer, int index, int n)
{
	if(index == n)
	{
		for(int i = 0; i < n; i ++)
			cout << c[number[i]][answer[i]];
		cout << "\n";
		return;
	}

	for(answer[index] = 0; answer[index] < total[number[index]]; answer[index] ++)
	{
		RecursiveSearch(c, total, number, answer, index + 1, n);
	}
}

解法二：递归方法 

#include<iostream>
#include<stdio.h>

using namespace std;
#define TelLength 3
void RecursiveSearch(char c[10][10], int total[10],  int* number, int* answer, int index, int n);
int main()
{
	char c[10][10]= 
	{
			"",  //0
			"",  //1
			"ABC", //2
			"DEF", //3
			"GHI", //4
			"JKL", //5
			"MNO", //6
			"PQRS", //7
			"TUV", //8
			"WXYZ" //9
	};
	int total[10] = {0,0,3,3,3,3,4,3,4};
	int number[TelLength] = {4,2,7};
	int answer[TelLength] = {0,0,0};

	cout << "427" << "对应的所有英文是：\n";
	
	RecursiveSearch(c, total, number, answer, 0, TelLength);
	getchar();
	cout << "hello world!" << endl;
	return 0;
}

void RecursiveSearch(char c[10][10], int total[10], int* number, int* answer, int index, int n)
{
	if(index == n)
	{
		for(int i = 0; i < n; i ++)
			cout << c[number[i]][answer[i]];
		cout << "\n";
		return;
	}

	for(answer[index] = 0; answer[index] < total[number[index]]; answer[index] ++)
	{
		RecursiveSearch(c, total, number, answer, index + 1, n);
	}
}