编写一个方法,用来计算以下多项式的和,并输出1-1?2+1?3-1?4+...-1?50

float sum(int n) { int i; float total = 0; for (i = 1; i<=n; i++) if( i % 2 == 0) total -= 1/n; else total += 1/n; return total; }