求S=2+22+222+...n个2之值的算法..
#include<stdio.h>
#include<math.h>
void main()
{
double m,n,i,sum;
printf("please input number n:\n");
scanf("%d",&n);
if(n==1) sum=2;
else if(n>=2)
for (m=2,sum=2,i=2;i<=n;i++)
{
m=m+2*pow(10,(i-1));
sum=sum+m;
}
printf("%d",sum);
}
刚学习C自己想的,大家都来帮忙看下对不???

为什么用pow?

#include<stdio.h>
int main()
{
int a,n,m,sum,x;
printf("Please input two number: First is the cofficient; second is the frequency\n");
scanf("%d,%d",&a,&n);
for(m=1,sum=0;n>=0;n--)
{
x=a*m;
m=10*m+1;
sum+=x;
printf("%d+",x);
}
printf("=%d\n",sum);
getch();
return 0;
}

这是我写的，你自己去对照下看看对不对

应该不对吧。
给你改了一下：
#include<stdio.h>
#include<math.h>
void main()
{
double m,n,i,sum;
printf("please input number n:\n");
scanf("%lf",&n);
if(n==1) sum=2;
else if(n>=2)
for (m=2,sum=2,i=2;i<=n;i++)
{
m=m+2*pow(10,(i-1));
sum=sum+m;
}
printf("%lf",sum);
printf("\n");
}

t=sum=0;


t=t*11+m;
sum+=t;

#include<stdio.h>

int element(int n) //求出每一项的值
{
int element=2;
for(;n>1;n--)
{
element=element*10+2;
}
return element;
}

void main()
{
int n,temp,sum=0;
printf("Please input the number that you want to add up to:\n");
scanf("%d",&n);
for(;n>0;n--)
{
temp=element(n);
printf("%d+",temp); //输出计算式
sum+=temp; //求和
}
printf("=%d",sum); //输出加和
}