EXP

#include<stdio.h>
#include<math.h>
long double factorial(int itr)
{
    long double f=1.,i;
    for(i=1.;i<=itr;++i)
        f*=i;
    return f;
}
long double my_exp(double x)
{
    long double exp1=1.,exp2=0,eps;
    int itr=1;
    do
    {
      exp1+=pow(x,itr)/factorial(itr);
      eps=exp1-exp2;
      exp2=exp1;
      itr++;
    }
    while(fabs(eps)>1e-16);
    return exp1;
}
int main()
{
    double x;
    printf("Enter x: ");
    scanf("%lf",&x);
    printf("Library exp= %0.16lf\n",exp(x));
    printf("My exp     = %0.16Lf\n",my_exp(x));
}
/*
IO #1
Enter x: 5
Library exp= 148.4131591025765999
My exp     = 148.4131591025766034

IO #2
Enter x: 6.6678
Library exp= 786.6630406518070231
My exp     = 786.6630406518070064

IO #3
Enter x: 1
Library exp= 2.7182818284590451
My exp     = 2.7182818284590452
*/