Convert from any base to decimal and vice versa - GeeksforGeeks

Convert from any base to decimal and vice versa - GeeksforGeeks
Given a number and its base, convert it to decimal. The base of number can be anything such that all digits can be represented using 0 to 9 and A to Z. Value of A is 10, value of B is 11 and so on. Write a function to convert the number to decimal.

int val(char c)

{

    if (c >= '0' && c <= '9')

        return (int)c - '0';

    else

        return (int)c - 'A' + 10;

}

 

// Function to convert a number from given base 'b'

// to decimal

int toDeci(char *str, int base)

{

    int len = strlen(str);

    int power = 1; // Initialize power of base

    int num = 0;  // Initialize result

    int i;

 

    // Decimal equivalent is str[len-1]*1 +

    // str[len-1]*base + str[len-1]*(base^2) + ...

    for (i = len - 1; i >= 0; i--)

    {

        // A digit in input number must be

        // less than number's base

        if (val(str[i]) >= base)

        {

           printf("Invalid Number");

           return -1;

        }

 

        num += val(str[i]) * power;

        power = power * base;

    }

 

    return num;

}

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