octal_to_decimal.c

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

// Converts octal number to decimal
int convertValue(int num, int i) {
    return num * pow(8, i);
}

long long toDecimal(int octal_value) {

    int decimal_value = 0, i = 0;

    while (octal_value) {

        // Extracts right-most digit and then multiplies by 8^i
        decimal_value += convertValue(octal_value % 10, i++);

        // Shift right in base 10
        octal_value /= 10;
    }

    return decimal_value;
}

int main() {

    printf("Enter octal value: ");

    int octal_value;

    scanf("%d", &octal_value);

    long long result = toDecimal(octal_value);

    printf("%d in decimal is %lld\n", octal_value, result);

    return 0;
}