mickyconv.c

#include <stdio.h>
#include <string.h>
#include <assert.h>

static char digits [] = "0123456789" ;
static char separator = ',' ;

static void reverse (char *start, char *last) {
    while (start < last) {
        char tmp = *start ;
        *start = *last ;
        *last = tmp ;
        ++start ;
        --last ;
    }
}

static char *   mickeyconv (char *dst, int value, unsigned int group_size) {
    unsigned int rem = 0 ;
    unsigned int v ;
    if (value < 0) {
        v = (unsigned int)-value ;
    }
    else {
        v = (unsigned int)value ;
    }
    int length = 0 ;
    do {
        rem = v % 10;
        v /= 10 ;
        if (length % (group_size + 1) == 0) {
            // Note: Emitted 0th separator is nuked after reversing
            dst [length++] = separator ;
        }
        dst [length++] = digits [rem] ;
    } while (0 < v) ;
    if (value < 0) {
        dst [length++] = '-' ;
    }
    // At this point, `dst` contains a delimited digits w/ prepended superfluous separator in reverse order
    reverse (dst, dst + length - 1) ;
    dst [length - 1] = 0 ;  // Overwrite superfluous separator.
    return dst ;
}

static int test (const char *expected, const char *actual) {
    if (strcmp (actual, expected) == 0) {
        return 1 ;
    }
    fprintf (stderr, "Expected: \"%s\"\n", expected) ;
    fprintf (stderr, " But got: \"%s\"\n", actual) ;
    assert (0) ;
}

int main () {
    char buf [256] ;
    test (             "0", mickeyconv (buf,           0, 3)) ;
    test (            "10", mickeyconv (buf,          10, 3)) ;
    test (           "100", mickeyconv (buf,         100, 3)) ;
    test (         "1,000", mickeyconv (buf,        1000, 3)) ;
    test (        "10,000", mickeyconv (buf,       10000, 3)) ;
    test ( "1,234,567,890", mickeyconv (buf,  1234567890, 3)) ;
    test (           "-10", mickeyconv (buf,         -10, 3)) ;
    test (          "-100", mickeyconv (buf,        -100, 3)) ;
    test (        "-1,000", mickeyconv (buf,       -1000, 3)) ;
    test (       "-10,000", mickeyconv (buf,      -10000, 3)) ;
    test ("-1,234,567,890", mickeyconv (buf, -1234567890, 3)) ;

    test (            "0", mickeyconv (buf,           0, 4)) ;
    test (           "10", mickeyconv (buf,          10, 4)) ;
    test (          "100", mickeyconv (buf,         100, 4)) ;
    test (         "1000", mickeyconv (buf,        1000, 4)) ;
    test (       "1,0000", mickeyconv (buf,       10000, 4)) ;
    test ( "12,3456,7890", mickeyconv (buf,  1234567890, 4)) ;
    test (          "-10", mickeyconv (buf,         -10, 4)) ;
    test (         "-100", mickeyconv (buf,        -100, 4)) ;
    test (        "-1000", mickeyconv (buf,       -1000, 4)) ;
    test (      "-1,0000", mickeyconv (buf,      -10000, 4)) ;
    test ("-12,3456,7890", mickeyconv (buf, -1234567890, 4)) ;
    return 0;
}