mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
23 lines
488 B
C++
23 lines
488 B
C++
#include <math.h>
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#include <stdio.h>
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int main(void)
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{
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int x[3], y[3], n;
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double sum;
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while (scanf("%d", &n), n)
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{
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scanf("%d%d", x, y);
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x[2] = x[0]; y[2] = y[0];
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sum = 0.0;
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while (--n)
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{
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scanf("%d%d", x+1, y+1);
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sum += x[0]*y[1] - x[1]*y[0];
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x[0] = x[1]; y[0] = y[1];
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}
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sum += x[0]*y[2] - x[2]*y[0];
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printf("%.1f\n", sum / 2.0);
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}
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return 0;
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}
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