>>252
とりあえずカンマ入れるモードだけ作った。

int YenConvert(int kingaku, int mode, char *buffer, int result)
{
int min_buf_size, tmp, sign, digit;
char *p;

/* */
if (!buffer) return -3;

/* mode check */
if (mode != 1 && mode != 2) return -1;

/** calc required buf size by kingaku **/
/* get sign */
sign = kingaku < 0 ? -1: 1;
/* abs */
kingaku = kingaku < 0 ? -kingaku : kingaku;
/* digit */
tmp = kingaku / 10;
digit = 1;
while(tmp > 0) {
digit++;
tmp /= 10;
}
/* buf size */
min_buf_size = 1; /* nul terminator */
if (sign == -1) min_buf_size++;
min_buf_size += digit + (digit-1)/3;