c语言sin函数

#include "stdio.h"
#include "math.h"
#define pai 3.14159265358979
#define pai 3.14159265358979
double jiecheng(double a)
{
double ai;
if(a==1)
{return 1;}
ai=a*jiecheng(a-1);
return(ai);
}
double sin0pai2(double a)
{
double ai=0.0;int i,e=1;
for(i=1;;i++)
{
ai+=(e/(jiecheng(2*i-1)))*(pow(a,2*i-1));
e=e*(-1);
if((pow(a,2*i+1))/(jiecheng(2*i+1))<0.00000000001)
{break;}
}
return(ai);
}
double sind02(double a)
{
double ai;
if(2*pai<=a)
{
while(a>=2*pai)
{a=a-2*pai;}
if(a==0)
{return 0;}
if(a==(pai/2))
{return 1;}
if(a==pai)
{return 0;}
if(a==pai/2*3)
{return -1;}
}
if(0{
ai=sin0pai2(a);
return(ai);
}
if((pai/2){
a=pai-a;
ai=sin0pai2(a);
return(ai);}
if(pai{
a=a-pai;
ai=sin0pai2(a);
return((-ai));
}
if(pai/2*3{
a=2*pai-a;
ai=sin0pai2(a);
return((-ai));
}
}

double sin2(double a)
{
double ai;
if(a>=0)
{ai=sind02(a);
return(ai);
}
if(a<0)
{
a=-a;
ai=sind02(a);
return(-ai);
}
}
main()
{
double a,b,c;
printf("inputh the data\n");
scanf("%lf",&a);
c=a/180*pai;
b=sin2(c);
printf("sin%lf=%lf",a,b);
}