本题要求编写程序，计算交错序列 1-2/3+3/5-4/7+5/9-6/11+... 的前N项之和。c语言

#include <stdio.h>

int main()
{
int n, i;
float sum = 0, sign = 1, numerator = 1, denominator = 3;

printf("请输入要计算的项数N：");
scanf("%d", &n);

for (i = 1; i <= n; i++)
{
sum += sign * numerator / denominator;
sign = -sign;
numerator += 2;
denominator += 2;
}

printf("前%d项的和为%.2f\n", n, sum);

return 0;
}