POJ NO.2105 IP Address（POJ 2105 IP地址转换）

POJ NO.2105 IP Address

Description

Suppose you are reading byte streams from any device, representing IP addresses. Your task is to convert a 32 characters long sequence of '1s' and '0s' (bits) to a dotted decimal format. A dotted decimal format for an IP address is form by grouping 8 bits at a time and converting the binary representation to decimal representation. Any 8 bits is a valid part of an IP address. To convert binary numbers to decimal numbers remember that both are positional numerical systems, where the first 8 positions of the binary systems are: 

2^7   2^6  2^5  2^4  2^3   2^2  2^1  2^0 

128    64   32   16   8     4    2    1 

Input

The input will have a number N (1<=N<=9) in its first line representing the number of streams to convert. N lines will follow.

Output

The output must have N lines with a doted decimal IP address. A dotted decimal IP address is formed by grouping 8 bit at the time and converting the binary representation to decimal representation.

Sample Input

4

00000000000000000000000000000000 

00000011100000001111111111111111 

11001011100001001110010110000000 

01010000000100000000000000000001 

Sample Output

0.0.0.0

3.128.255.255

203.132.229.128

80.16.0.1

-------------------------------------------------------------------------

大概的意思是把32位的二进制数转换成用小数点（.）隔开的十进制表示的IP地址。

解答一：每次读入8个字符后转换成十进制数。一行是32个字符，需要处理4次，中间还要添加3次小数点。

#include<stdio.h>int main(){//freopen("input.txt","r",stdin);int i,j,k;int n;scanf("%d\n",&n);for(i=0;i<n;i++){for(j=0;j<4;j++){int d=128,t=0;for(k=0;k<8;k++){char c=getchar()%48;//c=1 or 0，查ASCII码可知t+=d*c;d/=2;}if(j<3)printf("%d.",t);elseprintf("%d\n",t);}}return 0;}

解答二：使用strtol函数，将字符数组直接转换成十进制。

#include<stdio.h>#include<stdlib.h>int main(){//freopen("input.txt","r",stdin);int i,j;int n;scanf("%d\n",&n);for(i=0;i<n;i++){for(j=0;j<4;j++){char str[9];int t;scanf("%8s",str);t=strtol(str,0,2);if(j<3)printf("%d.",t);elseprintf("%d\n",t);}}return 0;}

扩展：将一个32位的无符号整型数变换成IP地址，比如

1988，表示成无符号整型为00000000 00000000 00000111 11000100，转换成IP：0.0.7.196

#include<stdio.h>int main(){//freopen("input.txt","r",stdin);int i,j;unsigned int n,a,t;scanf("%u\n",&n);for(i=0;i<n;i++){scanf("%u",&a);for(j=0;j<4;j++){t=(a&0xff000000)>>24;//将32位二进制从左到右每次取8位a<<=8;if(j<3)printf("%u.",t);elseprintf("%u\n",t);}}return 0;}