#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int string_to_int(const char* s, int* n, int base);
int string_to_unsigned(const char* s, unsigned int* n, int base);
int string_to_long(const char* s, long int* n, int base);
int string_to_unsigned_long(const char* s, unsigned long int* n, int base);
int string_to_double(const char* s, double* n);

/**
 * Convert a string to an int.  If you pass in a <code>base</code> of
 * zero, the conversion will treat a leading "0x" prefix as
 * hexadecimal and a leading "0" prefix as octal.
 *
 * @param[in] s string to convert
 * @param[out] n conversion of <code>s</code> to an unsigned long
 * @param[in] base base to use for the conversion
 * @return 1 on success and 0 on error
 */
int string_to_int(const char* s, int* n, int base)
{
    int rv = 0;
    long int tmp = 0;
    if (string_to_long(s, &tmp, base)) {
        if ((tmp >= INT_MIN) && (tmp <= INT_MAX)) {
            *n = (int)tmp;
            rv = 1;
        }
    }
    return rv;
}

/**
 * Convert a string to an unsigned.  If you pass in a
 * <code>base</code> of zero, the conversion will treat a leading "0x"
 * prefix as hexadecimal and a leading "0" prefix as octal.
 *
 * @param[in] s string to convert
 * @param[out] n conversion of <code>s</code> to an unsigned int
 * @param[in] base base to use for the conversion
 * @return 1 on success and 0 on error
 */
int string_to_unsigned(const char* s, unsigned int* n, int base)
{
    int rv = 0;
    unsigned long int tmp = 0;
    if (string_to_unsigned_long(s, &tmp, base)) {
        if (tmp <= UINT_MAX) {
            *n = (unsigned int)tmp;
            rv = 1;
        }
    }
    return rv;
}

/**
 * Convert a string to a long.  If you pass in a <code>base</code> of
 * zero, the conversion will treat a leading "0x" prefix as
 * hexadecimal and a leading "0" prefix as octal.
 *
 * @param[in] s string to convert
 * @param[out] n conversion of <code>s</code> to a long int
 * @param[in] base base to use for the conversion
 * @return 1 on success and 0 on error
 */
int string_to_long(const char* s, long int* n, int base)
{
    int rv = 0;
    long int tmp = 0;
    char* first_bad_char = NULL;
    const char* r = NULL;     /* Remainder of the string.     */

    /* You have to manually check for an empty string. */
    for ( ; *s != '\0' ; ++s) {
        if (!isspace(*s)) {
            break;
        }
    }
    if (*s == '\0') {
        goto done;
    }

    /* Do the conversion. */
    errno = 0;
    tmp = strtol(s, &first_bad_char, base);

    /* Check for errors. */
    if (errno) {
        goto done;
    }
    /* Allow trailing space. */
    r = first_bad_char;
    for ( ; *r != '\0' ; ++r) {
        if (!isspace(*r)) {
            break;
        }
    }
    if (*r != '\0') {
        goto done;
    }

    /* Success. */
    *n = tmp;
    rv = 1;

 done:
    return rv;
}

/**
 * Convert a string to an unsigned long.  If you pass in a
 * <code>base</code> of zero, the conversion will treat a leading "0x"
 * prefix as hexadecimal and a leading "0" prefix as octal.
 *
 * @param[in] s string to convert
 * @param[out] n conversion of <code>s</code> to an unsigned long int
 * @param[in] base base to use for the conversion
 * @return 1 on success and 0 on error
 */
int string_to_unsigned_long(const char* s, unsigned long int* n, int base)
{
    int rv = 0;
    int is_negative = 0;
    unsigned long int tmp = 0;
    char* first_bad_char = NULL;
    const char* r = NULL;     /* Remainder of the string.     */

    /* You have to manually check for a leading minus sign or an empty
     * string. */
    for ( ; *s != '\0' ; ++s) {
        if (!isspace(*s)) {
            break;
        }
    }
    if (*s == '\0') {
        goto done;
    }

    /* You want to allow "-0" to succeed.  So we have to wait to see
     * how the conversion goes. */
    if (*s == '-') {
        is_negative = 1;
    }

    /* Do the conversion. */
    errno = 0;
    tmp = strtoul(s, &first_bad_char, base);

    /* Check for errors. */
    if (errno) {
        goto done;
    }
    /* Allow trailing space. */
    r = first_bad_char;
    for ( ; *r != '\0' ; ++r) {
        if (!isspace(*r)) {
            break;
        }
    }
    if (*r != '\0') {
        goto done;
    }

    /* Only "-0" is allowed. */
    if (is_negative && (tmp != 0)) {
        goto done;
    }

    /* Success. */
    *n = tmp;
    rv = 1;

 done:
    return rv;
}

/**
 * Convert a string to a double.  The conversion will treat a leading
 * "0x" prefix as hexadecimal floating point and a leading "0" prefix
 * as octal floating point.
 *
 * @param[in] s string to convert
 * @param[out] n conversion of <code>s</code> to a double
 * @return 1 on success and 0 on error
 */
int string_to_double(const char* s, double* n)
{
    int rv = 0;
    double tmp = 0.0;
    char* first_bad_char = NULL;
    const char* r = NULL;     /* Remainder of the string.     */

    /* You have to manually check for an empty string. */
    for ( ; *s != '\0' ; ++s) {
        if (!isspace(*s)) {
            break;
        }
    }
    if (*s == '\0') {
        goto done;
    }

    /* Do the conversion. */
    errno = 0;
    tmp = strtod(s, &first_bad_char);

    /* Check for errors. */
    if (errno) {
        goto done;
    }
    /* Allow trailing space. */
    r = first_bad_char;
    for ( ; *r != '\0' ; ++r) {
        if (!isspace(*r)) {
            break;
        }
    }
    if (*r != '\0') {
        goto done;
    }

    /* Success. */
    *n = tmp;
    rv = 1;

 done:
    return rv;
}

int main(int argc, char* argv[])
{
    int rv = 0;
    double n = 0;
    char* nl = NULL;  /* new line character */
    char line[1024];

    while (fgets(line, sizeof(line), stdin) != NULL) {
        /* Remove trailing new line character. */
        if ((nl = strrchr(line, '\n')) != NULL) {
            *nl = '\0';
        }
        /* Look for the exit. */
        if ((strcmp(line, "quit") == 0) || (strcmp(line, "exit") == 0)) {
            break;
        }
        /* Try to convert input. */
        if (string_to_double(line, &n)) {
            printf("\"%s\" --> %.6g\n", line, n);
        } else {
            printf("Unable to convert: \"%s\"\n", line);
        }
    }

    return rv;
}