编译没错！运行错误！大家指点一下

#include "iostream.h"
#include "stdlib.h"
#include "math.h"
double sin(int a);
double sqrt(double a);
double cosn(int a);
int main()
{
    const double pi=3.14f;
    int a;
    cout<<"请输入角度：";
    cin>>a;
    cout<<cosn(a)<<endl;
    return 0;
}
double cosn(int a)
{
    const double pi=3.14f;
    double sum;
    sum=sqrt(1-sin(a/360*2*pi)*sin(a/360*2*pi));
        return sum;
}


没次运行都是1！！！怎么回事啊？

[[it] 本帖最后由 lockhawk 于 2008-9-23 18:14 编辑 [/it]]