程序代码：

root@~ #cat stob.c
#include <stdio.h>
#include <string.h>

int main (void) {

        char str[10],*p=str;
        int a[32],i=0,j=1,k,sum=0,l=0,*s=a;

//input hex string
        printf("Enter a Hex-string:");
        gets(p);

//point to the right of character
        p=str+strlen(p)-1;

//From character to integer,Result in Sum.
        while(*p) {
                if(*p>='0'&&*p<='9') {
                        sum+=(*p-'0')*j;
                }
                else if(*p>='a'&&*p<='f') {
                        sum+=(*p-'a'+10)*j;
                }
                else {
                        printf("Input Error! Exit!\n");
                        return -1;
                }
                j*=16;
                p--;
        }

//Convert to binary array,Reslut in a[]
        do {
                a[i]=sum%2;
                sum/=2;
                i++;
        }while(sum!=0);

//Reverse array
        j=i-1;
        for(k=0;k<=j/2;k++,j--) {
                sum=a[k];
                a[k]=a[j];
                a[j]=sum;
        }

//Display binary array
        printf("%s's binary is : ",str);
        while(l<i) printf("%i",*(s+l++));
        printf("\n");

        return 0;

}
测试：
root@~ #./stob
Enter a Hex-string:f
f's binary is : 1111
root@~ #./stob
Enter a Hex-string:1234abcd
1234abcd's binary is : 10010001100101010011111001101
root@~ #./stob
Enter a Hex-string:sdf4
Input Error! Exit!
root@~ #./stob
Enter a Hex-string:ffff
ffff's binary is : 1111111111111111
root@~ #

程序代码：

//Reverse array
        j=i-1;
        for(k=0;k<(i-1)/2;k++,j--) {
                sum=a[k];
                a[k]=a[j];
                a[j]=sum;
        }