c语言没有次方符号

<span style="color:#33FF33;">#include<stdio.h>
#include<math.h>

int main(void)
{
double a,b,sum,tmp;
int i;
a = 1;
b = 2;
sum = 0;
for (i = 2; i <= 20; ++i)
{
tmp = a + b;
a = b;
b = tmp;
sum = sum + pow(-1,i)*(a / b);//pow包含在math.h中

}
sum = sum + 0.5;

}
</span><p><span style="color:#33FF33;">原型：在TC2.0中原型为extern float pow(float x, float y); ，而在VC6.0中原型为double pow( double x, double y );</span></p><p><span style="color:#33FF33;">头文件：<a target=_blank href="http://baike.baidu.com/view/673537.htm" target="_blank">math.h</a>/<a target=_blank href="http://baike.baidu.com/view/3801631.htm" target="_blank">cmath</a>(<a target=_blank href="http://baike.baidu.com/view/824.htm" target="_blank">C++</a>中)</span></p><p><span style="color:#33FF33;">功能：计算x的y次<a target=_blank href="http://baike.baidu.com/view/270396.htm" target="_blank">幂</a>。</span></p><p><span style="color:#33FF33;">返回值：x不能为负数且y为小数，或者x为0且y小于等于0，返回幂指数的结果。</span></p><p><span style="color:#33FF33;">返回类型：<a target=_blank href="http://baike.baidu.com/view/860124.htm" target="_blank">double</a>型，int，float会给与警告！</span></p>