36 lines
853 B
C
36 lines
853 B
C
#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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double pi(double tolerance)
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{
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double x, y, val, error;
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unsigned long sampled = 0, hit = 0, i;
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do {
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/* don't check error every turn, make loop tight */
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for (i = 1000000; i; i--, sampled++) {
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x = rand() / (RAND_MAX + 1.0);
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y = rand() / (RAND_MAX + 1.0);
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if (x * x + y * y < 1) hit ++;
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}
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val = (double) hit / sampled;
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error = sqrt(val * (1 - val) / sampled) * 4;
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val *= 4;
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/* some feedback, or user gets bored */
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fprintf(stderr, "Pi = %f +/- %5.3e at %ldM samples.\r",
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val, error, sampled/1000000);
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} while (!hit || error > tolerance);
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/* !hit is for completeness's sake; if no hit after 1M samples,
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your rand() is BROKEN */
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return val;
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}
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int main()
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{
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printf("Pi is %f\n", pi(3e-4)); /* set to 1e-4 for some fun */
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return 0;
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}
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