【少年黑客第一季04】循环出错

#include<cstdio>

int main ()

{

 int s,c;

 scanf("%d",&a);

 int b=0;

 do{    

       b++;

   c=c+b;

 }while(b<a)

 printf("%d",c)

return 0;

}

信息：

E:\xxxx\xxxx\xxxx\xxxx  In function 'int main()':

515E:\xxxx\xxxx\xxxx\xxxx  计算s=1+2+3+……+n.cpp[Error] 'a' was not declared in this scope

113E:\xxxx\xxxx\xxxx\xxxx  [Error] expected ';' before 'printf'

122E:\xxxx\xxxx\xxxx\xxxx  [Error] expected ';' before 'return'