单表代换密码（初具形式）.cpp

密码学的一个实验:单表代换密码算法源程序.代码不长,本连工程文件一起发上来.请慢用,呵呵~

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
main()
{
	char str[256],z[26],code[256],plaintext[256],ciphertext[256];
	char *p=str; char *q=str,*r=z,*s=plaintext,*t=ciphertext;
	char c,d,e,f;
	int l,i;
    for( i=0;i<26;i++)
		z[i]=i+97;
	printf("Array z is:\n");
	for(i=0;i<26;i++)
		printf("%c",z[i]);
loop2:printf("\nPlease input the key:\n");
	gets(str);
	l=strlen(str);
		printf("the length of str(key) is:%d\n",l);
	loop:for(i=0;i<l;i++)
	{   
		int j=i+1;
        for(;j<l;j++)
		{
			if(i!=j&&p[i]==q[j])
			{
				for(;j<l;j++)

					q[j]=q[j+1];//写成q[j+1]=q[j]; 是错误的！！！
				l--;
			
				goto loop;

			}
			else ;
		}
	}
	printf("here the key is changed to:\n");
	for(i=0;i<l;i++)
		printf("%c",p[i]);
	l=strlen(str);
	printf(" now the length of Arrazy str(key) is changed to: %d\n",strlen(str));

	//************
	int n=0,k=l;
	

loop1:for(i=n;i<26;i++)
	  {
		
		for(int j=0;j<k;j++)
		{
			if(p[j]==r[i])
			{
				n++;goto loop1;
			}
		}
		str[k++]=z[i];
	  }
      printf("\ntable done!\n");
	  printf("\n***************************\n");
      for(i=0;i<26;i++)
		printf("%c",r[i]); printf("\n");
      for(i=0;i<26;i++)
		printf("%c",p[i]);  printf("\n"); 
	   printf("***************************\n");
	  
	  printf("please input plaintext: ");
	  gets(plaintext);printf("\n");
	  puts(plaintext);
	  printf("You hava just input the plaintext,are you sure to do encryption?(y/n)");
	  c=getchar();
	  if(c=='n') exit(0);
	  else if(c!='y')
					{
				       printf("input your choice again!");
				       c=getchar();
					}
	  for(i=0;i<(int)strlen(plaintext);i++)
		  for(int j=0;j<26;j++)
			  if(s[i]==r[j])
				  code[i]=p[j];
			  for(i=0;i<(int)strlen(plaintext);i++)
				  printf("%c",code[i]);
			   printf("\ncontinue?(y/n)");
			   d=getchar();
	           if(d=='n') exit(0);
			   else if(c!='y')
					{
				       printf("input your choice again!");
				       d=getchar();
					}

			   printf("please input ciphertext");
			   gets(ciphertext);printf("\n");
			   puts(ciphertext);
			   printf("You hava just input the ciphertext,are you sure to do decryption?(y/n)");
			   e=getchar();
			   if(e=='n') exit(0);
			   else if(c!='y')
			   {
				   printf("input your choice again!");
				   e=getchar();
			   }
			   //********************decryption
			   for(i=0;i<(int)strlen(ciphertext);i++)
		          for(int j=0;j<26;j++)
			      if(t[i]==s[j])
				    code[i]=z[j];
			        for(i=0;i<(int)strlen(ciphertext);i++)
				    printf("%c",code[i]);
			        printf("continue?(y/n)");
					f=getchar();
                    if(f=='n') exit(0);
			        else if(c!='y')
					{
				       printf("input your choice again!");
				       f=getchar();
					}
					else goto loop2;
			  


	  
		  
	  return 0;

}