xiangnong.cpp

用C++实现香农编码过程,对各概率排序,计算码字,码长,最后实现编码

#include<iostream>
#include<string>
#include<cmath>
using namespace std;
#define MAX 1000  
struct
{
	double x;//字符概率
    double y;//字符概率类加
	int k;//码字长度
    int code; /*第i个消息符号的码字*/
}x[MAX];
void  xi(double a[],int n)
{                                
    int i,j,max;
    double I=0,t,p=0;
	for(i=0;i<n;i++){  x[i].x=a[i];}

    cout<<"信源符号按概率从大到小排列:"<<endl;
    for(i=0;i<n;i++)
	{ max=i;
      for(j=i+1;j<n;j++)
	  {   
		 if(x[i].x<=x[j].x)
		    max=j; 
            t=x[i].x;
            x[i].x=x[max].x;
			x[max].x=t;
	  }
	} 
    for(i=0;i<n;i++)
	{ cout<<x[i].x<<"\t";}
	cout<<endl;
    cout<<"信源符号求累加和"<<endl;
    for(i=0;i<n;i++)
	{   
	 if(i!=0){ p+=x[i-1].x;x[i].y=p;}
	 else x[i].y=0;
	 cout<<"Pa(x"<<i+1<<")="<<x[i].y<<endl;}
	cout<<"码字长度:"<<endl;
    for(i=0;i<n;i++)
	{ 
	  I=-log(x[i].x)/log(2);
	  if(I-(int)I==0){x[i].k=(int)I;}
	  else x[i].k=(int)I+1;
    cout<<"k"<<i+1<<"="<<x[i].k<<endl;
	}
    cout<<"码字:"<<endl;
    for(i=0;i<n;i++)
	{    double t=1;
		for(j=0;j<x[i].k;j++)
		{   t=t*0.5;
			x[i].y=x[i].y-t;
         if(x[i].y>=0) printf("1");
         if(x[i].y<0) {x[i].y=-x[i].y;printf("0");}
		}
		cout<<endl;
	}
    
}
void input()
{
    int i,m;	
	double sum=0;
	double a[MAX];
	cout<<"输入信源个数:";
    cin>>m; 
    cout<<"输入"<<m<<"个该信源概率:"<<endl;
    for(i=0;i<m;i++){ cout<<"P(x"<<i+1<<"):";cin>>a[i]; sum=sum+a[i];}
    if(sum!=1)
     {	cout<<"输入概率和是"<<sum<<"不为1，请重输";
       a[m]=NULL;
      input();
     }
    else xi(a,m);
}
void main()
{   cout<<endl<<"    \t\t\t \25 香农编码计算 \25"<<endl<<endl;
    input();
  cout<<endl;
}