Taylor series expansion of cos(x) is not working

#include <stdio.h>
#include <math.h>
#define PI 3.1416
double fact(n){
  double x = 1;
  for(int i = 1 ; i <= n ; i++){
    x = x*i;
  }
  return x;
}
int main(void) {
  int deg,term,n=1,sign=1;
  float radian,result=0;
  printf("Enter the Angle (in degree) : ");
  scanf("%d",&deg);
  printf("Enter the number of terms : ");
  scanf("%d",&term);
  radian = deg*(PI/180.0);

  for(int count = 0 ;n<=term ; count+=2){
    result = result + sign *(double)(pow(radian,count)/fact(count));
    n++;
    sign = sign * (-1) ;
  }
  
  printf("user defined cos(%d) = %f\n",deg,result);
  printf("inbuilt cos(%d) = %f\n",deg,cos(deg));
  return 0;
}

I tried similar code with sin function and with different value for count but its not working for cos. If anybody knows why its printing wrong answer... please reply

Your code is right, your test is wrong:

Instead of cos(deg), it should be cos(radian).

Moreover, instead of defining PI, you could use the one given in math.h: M_PI:

#define _USE_MATH_DEFINES
#include <math.h>

// from here, you can use M_PI 

You can also improve your code

1. Since cosine function is periodic and the Taylor series is better near 0, you should clamp the input number in [-180, 180] range

2. Factorial function could be computed faster: you have to compute 2!, 4!, 6!... if you store 4! for instance, 6! can be computed with only 2 multiplications instead or recomputing from the start (like you do for sign instead of calling pow(-1, n)

3. Same for the x^(2n)