factorial2.c

#include <stdio.h>
#include <math.h>

float factorial(int n){ // x!
  if(n == 0) return 1;
  else if(n < 0) return -1;
  int i = 1;
  int x = 1;
  for(i = 1; i <= n; i++) x = (float) x*i;
  return x;
}

float etaylor(int n){ // e = Σ1/(x!)
  if(n < 0) return -1;
  float x = 0;
  int i = 1;
  for(i = 1; i <= n; i++) x = x+(1.0/factorial(i));
  return x;
}

float extaylor(int x, int n){ // e^x = Σx/n!
  if(x < 0 || n < 0) return -1;
  int i = 0;
  float y = 0;
  for (i = 0; i <= (n-1); i++) y = y + pow(x,i)/factorial(i);
  return y;
}

int main(){
  int n, s, x;
  printf("WELCOME TO MY TAYLOR SERIES DUNGEON!!!1!!\n");
  printf("PLEASE SELECT YOUR CHALLENGE:\n");
  printf("1. y = x!\n");
  printf("2. e = E1/x!\n");
  printf("3. e^x = E[(x^k)/k!]\n");
  printf("Your selection: "); scanf("%d", &s);
  switch(s){ // Choose selection
    case 1: {
      printf("\nx = "); scanf("%d", &x);
      printf("\ny = %f", factorial(x));
      return 0;
    }
    case 2: {
      printf("\n x = "); scanf("%d", &x);
      printf("\n e = %f", etaylor(x));
      return 0;
    }
    case 3: {
      printf("\n x = "); scanf("%d", &x);
      printf("\n Upper bound k = "); scanf("%d", &n);
      printf("\n e^%d = %f", x, extaylor(x, n));
      return 0;
    }
    default: {
      printf("Invalid selection %d", s);
      return -1;
    }
  }
}