十六进制转八进制

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思路分析：

39十六进制先转换为4位二进制，3为0011，9为1001，所以39的二进制为00111001,又把二进制转化为3位八进制，从右边开始数，001为1，111为7，所以39的八进制为71。

#include <stdio.h>
#include <stdlib.h>
#include <string.h> 
#define MAX_SIZE 100000
/* run this program using the console pauser or add your own getch, system("pause") or input loop */int main(int argc, char *argv[]) {int n;      //十六进制数数量int i,j,k; // 计数变量 int result;int str_len;scanf("%d",&n);char str[n][MAX_SIZE];//建立数组，保存16个十六进制数对应的二进制数char demo[16][4] = {"0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"};memset(str,0,n*MAX_SIZE);  //将str初始化为0for(i=0;i<n;i++){scanf("%s",str[i]);k=0;str_len = strlen(str[i]);   //计数十六进制数长度 int ss = 4*str_len%3;         //判断转换后的二进制数数量是否为的倍数，如果不是，需要补0 char temp[4*str_len+3-ss];memset(temp,0,4*str_len+3-ss);if(ss == 1){strcat(temp,"00");k += 2;}if(ss == 2){strcat(temp,"0");k +=1;}/* 进行十六进制向二进制数的转换  */for(j=0;j<str_len;j++){if(str[i][j]<65){temp[k++] = demo[str[i][j]-48][0];temp[k++] = demo[str[i][j]-48][1];temp[k++] = demo[str[i][j]-48][2];temp[k++] = demo[str[i][j]-48][3];}else if(str[i][j]>=65){temp[k++] = demo[str[i][j]-55][0];temp[k++] = demo[str[i][j]-55][1];temp[k++] = demo[str[i][j]-55][2];temp[k++] = demo[str[i][j]-55][3];}}temp[k] = 0;//进行输出操作for(j=0;j<4*str_len;j+=3){if(j==0){result=(4*(temp[j]-48) + 2*(temp[j+1]-48) + (temp[j+2]-48));if( result != 0)printf("%d",result);}else{result=(4*(temp[j]-48) + 2*(temp[j+1]-48) + (temp[j+2]-48));printf("%d",result);}} printf("\n");} return 0;
}