求1-1/2+1/3-1/4+....+1/n的值，程序填空。int main(void){int i = 1,n,t=1;double sum = 0; //结果存放量scanf("%d",&n);//输入nwhile(i <= n){sum += t * (1.0 / i);i++;_______________//下一次符号变化值}printf("%.3lf",sum);return 0;}