等比数列：

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 代码实现

1-递推求和

#include<stdio.h>
int main()
{int n, i;double q, sum, temp;while (scanf("%d %lf", &n, &q) != EOF)//实现循环{sum = 1;temp = 1;for (i = 0; i < n; i++){temp *= q;//让临时变量第一次时等于q，以后的循环每次都乘qsum += temp;//累加}printf("%.3f\n", sum);}return 0;
}

2-借助公式

#include<stdio.h>
#include<math.h>
int main()
{double q,n,sum;while (scanf("%lf %lf", &n, &q) != EOF) //循环输入{if (q == 1){sum = n;}else { sum = (1 - pow(q, n + 1)) / (1 - q); }//等比数列求和公式printf("%.3lf\n", sum);}return 0;
}