C Program to convert octal to decimal

How to convert octal to decimal?
Octal value 756
(7 X 8^2) + (5 X 8^1) + (6 X 8^0) = (7 X 64) + (5 X 8) + 6 = 494
Multiply each digit with their corresponding power of 8 and calculate the sum of all.

Write a C program to convert octal number to decimal number

  #include <stdio.h>
  #include <math.h>
  #include <string.h>

  int main () {
        char data[10], ch;
        int val = 0, power = 0, i = 0, j = 0;

        /* get the octal input from the user */
        printf("Enter your octal value:");
        fgets(data, 10, stdin);
        data[strlen(data) - 1] = '\0';

        /* convert octal to decimal value */
        for (i = strlen(data); i > 0; i--) {
                ch = data[j++];
                power = pow(8, i - 1);
                if (ch >='0'&& ch <= '7') {
                        /* octal to decimal conversion */
                        val = val + (ch - '0') * power;
                } else {
                        /* value other than 0-7 are invalid */
                        printf("Wrong Input!!!\n");
                        return (-1);
                }
        }

        /* print the result */
        printf("Equivalent Decimal Value: %d\n", val);
        return 0;
  }

Note:
gcc oct2dec.c -lm => link math library since we have used pow() function.

  Output:

  jp@jp-VirtualBox:~/$ gcc oct2dec.c -lm
  jp@jp-VirtualBox:~/$ ./a.out
  Enter your octal value:756
  Equivalent Decimal Value: 494