01 #include <stdio.h>
02 #include <math.h>
03 #include <string.h>
04 
05 int main()
06 {
07     char hex[17];
08 
09     long int decimal=0, place=1;
10 
11     int i = 0, val, len,octal=0,remainder;
12 
13     printf("Enter any hexadecimal number: ");
14     gets(hex);
15 
16     /* length of hex digit */
17 
18     len = strlen(hex);
19     len--;
20 
21     /*hexa to decimal*/
22 
23     for(i=0; hex[i]!=''; i++)
24         {
25             switch(hex[i])
26                 {
27                 case '0':
28                     val = 0;
29                     break;
30                 case '1':
31                     val = 1;
32                     break;
33                 case '2':
34                     val = 2;
35                     break;
36                 case '3':
37                     val = 3;
38                     break;
39                 case '4':
40                     val = 4;
41                     break;
42                 case '5':
43                     val = 5;
44                     break;
45                 case '6':
46                     val = 6;
47                     break;
48                 case '7':
49                     val = 7;
50                     break;
51                 case '8':
52                     val = 8;
53                     break;
54                 case '9':
55                     val = 9;
56                     break;
57                 case 'a':
58                 case 'A':
59                     val = 10;
60                     break;
61                 case 'b':
62                 case 'B':
63                     val = 11;
64                     break;
65                 case 'c':
66                 case 'C':
67                     val = 12;
68                     break;
69                 case 'd':
70                 case 'D':
71                     val = 13;
72                     break;
73                 case 'e':
74                 case 'E':
75                     val = 14;
76                     break;
77                 case 'f':
78                 case 'F':
79                     val = 15;
80                     break;
81                 }
82 
83             decimal += val * pow(16, len);
84             len--;
85         }
86 
87     /*now decimal to octal*/
88 
89     i=1;
90     while(decimal != 0)
91         {
92             remainder = decimal%8;
93             octal = octal + (remainder*i);
94             decimal = decimal/8;
95             i = i*10;
96         }
97 
98     printf("Octal Number = %d",octal);
99     return 0;
100 }

 OUTPUT :
 
 Enter any hexadecimal number : A1
 Octal Number = 241