编程计算1－3＋5－7＋．．．－99

Answer 1

对，关键是算法。
直接可以求出前N项和公式.
int sum(int a) //a为最后一项,该例中为99
{
int sign;
if ((a+1)%4 ==0)
{
return -(a+1)/2;
}
else
{
return (a+1)/2;
}
}
main()
{
printf("%d\n",sum(99));
return 0;
}

Answer 2

Dim a As Integer
For i = 0 To 24
a = 1 + 4 * i + a
b = 3 + 4 * i + b
Next i
MsgBox a - b

Answer 3

#include <stdio.h>
int main()
{
int a,sign=1,sum=0;
for (a=1;a<100;a+=2)
{
sum+=sign*a; sign*=(-1);
}
printf("%d",sum);
return 0;
}

Answer 4

#include <iostream>
using namespace std;
void main()
{
int sum=0;
int aaa=1;
int n;
for(n=1;n<=50;n++)
{
sum=sum+(2*n-1)*aaa;
aaa=-aaa;
}
cout<<"1-3+5-7+...-99="<<sum<<endl;
}

Answer 5

我用的是C语言：
main()
{int a,sign=1,sum=0;
for (a=1;a<100;a+=2)
{sum+=sign*a;
sign*=(-1);
}
printf("%d",sum);
}