C 将一个数字字符串转换成这个字符串对应的数字（包括正浮点数、负浮点数）

double att(char *p)

{

int sum = 0;

int i = 0;

int a = 1;

double q;

if(*p == '-')

{

a = -1;

p++;

}

while(*p != '.')

{

sum = sum * 10 + (int)(*p - '0');

p++;

}

p++;

while(*p != '\0')

{

sum = sum * 10 + (int)(*p - '0');

p++;

i++;

}

q = (double)sum;

for(;i >= 0; i--)

{

q = q / 10;

}

q = q * a;

return q;

}