C语言程序：计算序列 2/1+3/2+5/3+8/5+... 的前N项之和

#include <stdio.h>

int main() { int n, i; double sum = 0.0, a = 2.0, b = 1.0, c;

scanf("%d", &n);

for (i = 1; i <= n; i++)
{
    sum += a / b;
    c = a;
    a = a + b;
    b = c;
}

printf(".2lf", sum);

return 0;

}