/* baseX-decimal-hw4.c
   Converts a base 64 number into decimal
   Created by Xiuwen Liu for Homework #4, Problem #1
*/
#include <ctype.h>
#include <stdio.h>
#include <string.h>
/* Based on the following base 64 encoding:
'0' to '9' map to 0 to 9
'A' to 'Z' map to 10 to 35
'a' to 'z' map to 36 to 61
'>' maps to 62
'?' maps tp 63
*/

int convert2dec64(char *str)
{
    int j, val, base, chval;
    base = 64;
    val = 0;
    j = 0;
    while (str[j] > 13) {
        if ( (str[j] > 47) && (str[j] < 58)) {
            chval =  str[j] - 48;
        }
        else if ( (str[j] > 64) && (str[j] < 91) ) {
            chval =  str[j]-55;
        }
        else if ( (str[j] > 96) && (str[j] < 123)) {
            chval = str[j] - 61;
        }
        else if ( (str[j] == 62) || (str[j] ==63) ) {
            chval =  str[j];
        } else {
            val = -1;
            break;
        }
        val = val * base + chval;
        j++;
    }
    return val;
}

int main(int argc, char *argv[])
{
    int X, res;
    char str[256];
    X = 64;
    printf("Please a number base %d: ", X);
    scanf("%s", str);
    res = convert2dec64(str);
    if (res != -1) {
        printf("The decimal value is %d\n", res);
    }
    else {
        printf("The input is not a valid base64 number.\n");
    }
    return 0;
}