习题2-4求交序列前N项和。#include<stdio.h> #include<math.h> int main() { int N,a,b,i; double sum; a=1,b=1,sum=0; printf("请输入一个正整数N\n"); scanf("%d",&N); for(i=1;i<=N;i++) {sum+=pow(-1.0,i+1)*a/b; a=a+1; b=b+2; } printf("sum=%.3f\n",sum); return 0; }