C语言计算圆周率PI

C语言计算圆周率PI

#include "stdio.h"  
#include "stdlib.h"  
  
#define SCALE 10000  
#define ARRINIT 2000  
  
void pi_digits(int digits) {  
    int carry = 0;  
    int arr[digits + 1];  
    for (int i = 0; i <= digits; ++i)  
        arr[i] = ARRINIT;  
    for (int i = digits; i > 0; i-= 14) {  
        int sum = 0;  
        for (int j = i; j > 0; --j) {  
            sum = sum * j + SCALE * arr[j];  
            arr[j] = sum % (j * 2 - 1);  
            sum /= j * 2 - 1;  
        }  
        printf("%04d", carry + sum / SCALE);  
        carry = sum % SCALE;  
    }  
}  
  
int main(int argc, char** argv) {  
    int n = argc == 2 ? atoi(argv[1]) : 100;  
    pi_digits(n);  
  
    return 0;  
}