char *F2S(double d, char *str) {

char str1[40];

int j = 0;

int k, i;

i = (int)d; // 浮点数的整数部分

while (i > 0) {

str1[j++] = i % 10 + '0';

i /= 10;

}

for (k = 0; k < j; ++k) {

str[k] = str[j - 1 - k];

str[j++] = '.';

for (i = 0; i < 10; ++i) {

d *= 10;

str[j++] = (int)d + '0';

d -= (int)d;

}

}

while (str[--j] == '0') {

str[++j] = '\0';

return str;

}

}