c 十六进制 转 十进制

 1 #include <stdio.h>
 2 #include <math.h>
 3 
 4 double
 5 hexToDecimal(int);
 6 
 7 double
 8 octToDecimal(int);
 9 
10 double
11 toDecimal(int, int, int);
12 
13 int
14 main(void) {
15     int a = 0x3c;
16     double r = hexToDecimal(a);
17     printf("%.f\n", r);
18     a = 017;
19     r = octToDecimal(a);
20     printf("%.f\n", r);    
21 }
22 
23 double
24 hexToDecimal(int hex) {
25     return toDecimal(hex, 15, 4);
26 }
27 double
28 octToDecimal(int oct){
29     return toDecimal(oct, 7, 3);
30 }
31 
32 
33 double
34 toDecimal(int num, int base, int offset) {
35     int i = 0;    //(b)的i次幂.
36     double r=0;    //十进制结果.
37     double b= base + 1;    //底数为b.
38     while(num) {
39         double t = (int)(num & base);
40         r += t * pow(b, i++);
41         num>>=offset;
42     }
43     
44     return r;
45 }