#include <string>
#include <sstream>
int main(){
  double a = 123.456;
  string res;
  stringstream ss;           // 定义流ss
  ss << a;                   // 将数字a转化成流ss
  ss >> res;                 // 将流ss转化成字符串
  return 0;
}

#include <string>
#include <sstream>
int main(){
  double a ;
  string res= "123.456";
  stringstream ss;  
  ss << res;                  
  ss >> a;
  return 0;
}
//此处包装了一个方法，将一位的数字转化成两位的字符串
// 比如说 ： 0->"00"    3->''03"
string transform(int num)
{
   string res;
   stringstream ss;
   ss<<num;
   ss>>res;
   if(num<10)
   {
    res="0"+res;
   }
   return res;
}

#include <iostream>
#include <string>
using namespace std;
int main()
{
    char str[10];
    int a=1234321;
    //将整数转化为字符串
    sprintf(str,"%d",a);
    int len=strlen(str);
    cout<<"字符串"<<str<<endl;
    cout<<"长度"<<len<<endl;
    char str1[10];
    double b=123.321;
    / /将浮点数转化为字符串
    sprintf(str1,"%.3lf",b);
    int len1=strlen(str1);
    cout<<"字符串"<<str1<<endl;
    cout<<"长度"<<len1<<endl;
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main()
{
    char str[]="1234321";
    int a;
    sscanf(str,"%d",&a);
    cout<<a<<endl;
    char str1[]="123.321";
    double b;
    sscanf(str1,"%lf",&b);
    cout<<b<<endl;
    return 0;
}