C :

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <iso646.h>
#include <math.h>
#include <malloc.h>

double fact(int m)
{
	int i;
	double s=1;
	for (i=1;i<=m;i++)
		s*=i;
	return s;
}

double mypow(double y,int m)
{
	double z;
	z=pow(y,m);
	return z;
}

int main()
{
	double x;
	int i,n;
	double ns,xs,s,sum=0;
	scanf ("%lf %d",&x,&n);
	
	for (i=1;i<=n;i++)
	{
		ns=fact(i);
		xs=mypow(x,i);
		s=xs/ns;
		if (i%2==0)
			s*=-1;
		sum+=s;
	}
	printf ("%.4lf\n",sum);

return 0;
}

C++ :

#include<stdio.h>
#include<math.h>
 
double fact(int n);
double mypow(double x,int  n);
int main() {
    double x, sum;
    int n;
 
    scanf("%lf", &x);
    scanf("%d", &n);
    sum = x;
    int i;
    for (i = 2; i <= n; i++) {
        sum = sum + pow(-1.0, i - 1) * mypow(x, i) / fact(i);
    }
 
    printf("%.4f", sum);
    return 0;
}
double fact(int n) {
    double fact = 1;
    int j;
    for (int j = 1; j <=n; j++) {
        fact = j * fact;
    }
    return fact;
}
double mypow(double x,int  n) {
    return pow (x, n);
}