C++第四次作业

#include <iostream>
using namespace std;
int main()
{
int a,b;
for(a=1;a<6;a++)
{
cout<<" ";
}
cout<<"*"<<endl;
for(a=2;a<6;a++)
{
for(b=0;b<6-a;b++)
{
cout<<" ";
}
cout<<"*";
for(b=0;b<2*(a-1)-1;b++)
{
cout<<" ";
}
cout<<"*"<<endl;
}
for(b=0;b<=2*a-2;b++)
{
cout<<"*";
}
cout<<endl;
return 0;
}

#include <iostream>
using namespace std;
int main()
{
int i,j,m;
for(i=1;i<=9;i++)
{
for(j=1;j<=i;j++)
{
m=j*i;
cout<<i<<'*'<<j<<'='<<m<<" ";
}
cout<<endl;
}
return 0;
}

#include<iostream>
using namespace std;
int main()
{
double i,k=1,j=0;
for(i=1;i<=19;i=i+2)
{
j=j+(i/(i+2))*k;
k=-k;
}
cout<<"j="<<j<<endl;
return 0;
}