The factorial of non-negative integer n is written n! and is
defined as follows:?
n! = n * (n – 1) * (n – 2) . …. .1 (for values of n greater
than or equal to 1).

and

n! = 1 (for n =0).

Perform the following:
a) Write a C program that reads a non-negative integer and
computes and prints its factorial.
b) Write a C program that estimates the value of the
mathematical constant e by using the formula: 

e = 1 + 1/1! + 1/2! + 1/3! + …..
c) Write a C program that computes the value ex by using the
formula 

ex= 1 + x/1! + x2/2! + x3/3! + …..

Answer:
a) int main()
{

int num;
long unsigned int factorial=1;

printf("Enter a number to compute factorial : ");
scanf("%d",&num);

for(int i=0;i<num;num--){
factorial *= num;
}

printf("The factorial is %d\n",factorial);
return 0;
}
//use upto num = 10 or 12 I guess

(b) For this 

int main(){
int num = 3;
float e_value=1;
float int factorial;

for(int i=0;i<num;num--){
factorial = 1;
for(int j=num;j>0;j--){
factorial *= j;
}
e_value += 1/factorial;
}
printf("The e value is %f\n",e_value);
return 0;
}

(c) for this the one you can figure out now I hope

int main(){
int num=3;
float e_value = 1;
float factorial;
int x;

printf("enter value of x : ");
scanf("%d",&x);

for(int i=0;i<num;num--){
factorial = 1;
for(int j=num;j>0;j--){
factorial *= j;
}
e_value += (x*num)/factorial;
}
printf("The value of ex is : %f",e_value);
return 0;
}

#include<stdio.h>
int main()
{
 int i,n,sum =0;
 printf("Enter value for n\n");
 scanf("%d",&n);
 sum = sum+1/fact(i);
 printf("sum of Total result %d",sum);
}

int fact(int j)
{
 int k =1;
 if(k <= j)
 fact = k*fact(--j);
 return fact;
}