#include<stdio.h>
#include<ctype.h>

int htoi( const char *s );

int main()
{
    char arr[4] = "0x3A";
    int result = htoi(arr);

    printf("%d\n", result);



    return 0;
}



int htoi( const char *s )
{
    int i, out;

    i = out = 0;

    //处理前缀
    if( s[0] == '0' && ( s[1] == 'x' || s[1] == 'X') )
        i = 2;

    //处理字符串
    while( s[i] != '\0' )
    {
        int tmp = 0;
        char c_tmp = s[i];

        if( isdigit(c_tmp) ){
            tmp = c_tmp - '0';
        }
        else if( c_tmp >= 'A' && c_tmp <= 'F' ){
            tmp = c_tmp - 'A' + 10;
        }
        else{
            puts("字符非法！");
        }

        out = out * 16 + tmp;
        ++i;
    }

    return out;
}