calc.c

#include <stdio.h>

double factorial(int n){
	if(n < 1){
		return 1;
	} else if(n == 1){
		return n;
	} else {
		return n * factorial(n - 1);
	}
}

double accumulate(double sum, int n){
	int sign = n % 2 == 0 ? 1 : -1;
	return sum + 1 / factorial(n) * sign;
}

double absDouble(double n){
	return n > 0 ? n : -n;
}

double fixedPoint(double lastTime, int n){
	double thisTime = accumulate(lastTime, n);
	if(absDouble(thisTime - lastTime) <= 0.000001){
		return thisTime;
	} else {
		return fixedPoint(thisTime, n + 1);
	}
}

double calc(){
	double num = 1.0;
	double ans = 1.0;
	double lastAns = 0.0;
	for(int i = 1; absDouble(lastAns - ans) >= 0.000001 ; ++i){
		lastAns = ans;
		num *= -1.0 / i;
		ans += num;
	}
	return ans;
}

int main(){
	printf("%f\n", fixedPoint(0, 0));
	printf("%f\n", calc());
	return 0;
}