calculo combinacao nk

# include<stdio.h>
# include<stdlib.h>
float fatorial(int);
float combinacao (int n, int a);
int main (void)
{
int n, k;
float fat, com;
printf("digite o valor de n\n");
scanf("%d",&n);
printf("digite o valor de k\n");
scanf("%d", &k);
com=combinacao(n,k);
printf("com de %d,%d e %f\n", n, k, com);
system("pause");
return 0;
}
float fatorial(int n)
{
float f=1;
int i;
for(i=1; i<=n; i++)
{
f=f*i;
}
return f;
}
float combinacao(int n, int k)
{
float c;
c=fatorial(n)/(fatorial(n-k)*fatorial(k));
return c;
}