It was written a long time ago , But my code hasn't improved much

Caesar encryption

#include<stdio.h>
#include<string.h>
void m();// menu 
void getinput(char input[]);// Get string 
void encrypt(char eninput[],char input[],char map[]);// encryption 
void decode(char deinput[],char input[],char map[]);// Decrypt 

int main()
{  int ch = 1;
   char input[1000];
   char eninput[1000];
   char deinput[1000];
   char map[26];
   int i = 0;
   for(i = 0;i<26;i++)
   {
   	map[i]='a'+i;
	
	}
   
	while(ch)
	{
		m();
		scanf("%d",&ch);
		if(ch==1)
		{
		 getinput(input);
		 
		}
		else if(ch==2)
		{
			encrypt(eninput,input,map);
		}
		else if(ch==3)
		{
			
			decode( deinput, input, map);
		}
		else break;
		
		
		
	}
	
	
	
	
	return 0;
	
}
void m()
{
	printf("----- Caesar encryption ---------\n");
	printf("-----1. Input string -----\n");
	printf("-----2. encryption -----------\n");
	printf("-----3. Decrypt -----------\n");
	printf("-----4. Exit procedure -------\n");
	printf(" Please enter :");
}
void getinput(char input[])
{
	printf(" Letters are encrypted and decrypted in lowercase \n");
	getchar();
	gets(input);
	
	
}
void encrypt(char eninput[],char input[] ,char map[])
{  
	printf(" Please enter the offset key(1,25):\n");
	int key;
	scanf("%d",&key);
	 int i = 0,j = 0;
	 for( i = 0;i<strlen(input);i++)
	 {
	 	for(j = 0;j<26;j++)
	 	{
		 	if((input[i]==map[j])||input[i]==(map[j]-32))
		 	{
		 		
			 	eninput[i]=((map[j]-'a')+key)%26+'a';// encryption 
			}
		 	
		}
	 	
	 }
	 eninput[i]='\0';
	 input[i]='\0';
	 printf(" Before encryption ：%s\n",input);
	 printf(" After encryption ：%s\n",eninput);
	 
	 
	
}
void decode(char deinput[],char input[],char map[])
{
	
		printf(" Please enter the offset key(1,25):\n");
		int key;
		scanf("%d",&key);
		 int i = 0,j = 0;
		 for( i = 0;i<strlen(input);i++)
		 {
		 	for(j = 0;j<26;j++)
		 	{
			 if(input[i]==map[j]||input[i]==map[j]-32)
			 {
			 	deinput[i]=((map[j]-'a')-key+26)%26+'a';// Decrypt 
			 }
			 	
			}
		 	
		 }
		    deinput[i]='\0';
		 	 input[i]='\0';
	     printf(" Before decryption ：%s\n",input);
		 printf(" After decryption ：%s\n",deinput);
	
	
}

Chessboard code

#include<stdio.h>
#include<string.h>
void m();
void f1(char map[6][6]);
void getstr(char str[]);
void encrypt(char input[],char map[][6]);// encryption 
void decode(char input[],char map[][6]);// Decrypt 
int main()
{   

	char input[1000];
	char map[6][6];
	f1(map);
	int a = 1;
	while(a)
	{
		m();
		scanf("%d",&a);
		if(a==0)
		break;
		else if(a==1)
		{
			encrypt(input, map);
	
		}
		else if(a==2)
		{
		 decode(input, map);
			
		}
		else{
			getstr(input);
		}
	
		
		
	}
		
	return 0;
	
	
	
	
	
}
void m()
{
	printf("-------- Chessboard code -------\n");
	printf("--------0. sign out ---------\n");
	printf("--------1. encryption ---------\n");
	printf("--------2. Decrypt ---------\n");
	printf("--------3. Get string ---\n");
	
}
void f1(char a[6][6])
{
	
	int i,j,z = 0;
	for(i = 1;i<=5;i++)
	{
		
		for(j = 1;j<=5;j++)
		{    if('a'+z=='j')  z++;
		 
			a[i][j]='a'+z++;
		}
	}
}
void getstr(char str[])
{
	getchar();
	gets(str);
	
}
void encrypt(char input[],char map[][6])
{ printf(" The chessboard encryption is as follows \n");
	int i,j,z;
	int flag = 0;
	for(i = 0;i < strlen(input);i++)
	{   flag = 1;
		for(j = 1;j<=5;j++)
		{
			if(flag == 0)
			 break;
			for(z = 1;z<=5;z++)
			{   if(input[i]=='j')
			{
				printf("%d%d ",2,4);
				 flag = 0;
				break;
				
			}
				if(map[j][z]==input[i])
				{
					 printf("%d%d ",j,z);
					 flag = 0;
					break;
				}
			}
		}
		
	}
	printf("\n");
	
	
}
void decode(char input[],char map[][6])
{    printf(" Do not enter blank spaces ,i And j You need to judge for yourself \n");
		int i;
	    
		for(i = 0;i<strlen(input);i=i+2)
		{   
		printf("%c",map[input[i]-'0'][input[i+1]-'0']);
			
		}
		printf("\n");
	
}

Fence code

#include<stdio.h>
#include<string.h>
void encrypt(char str[10000]);
void m();
void decrypt(char str[10000]);



int main() {


	char str[10000];
	int c = 1;
	while (c) {
		m();
		printf(" Please enter your choice :");
		scanf("%d", &c);
		getchar();
		if (c == 1) {
			encrypt(str);
		} else if (c == 2) {
			decrypt(str);
		}

	}

	return 0;


}
void encrypt(char str[10000]) {
	printf(" Please enter the string ：\n");
	gets(str);
	int a;
	printf(" Please enter the number of fences :");
	scanf("%d", &a);
	char t[1000][1000];
	int len = strlen(str);
	int i, j;
	int h = len / a, s = len % a;
	if (s != 0) h++;
	int z = 0;
	for (i = 0; i < h; i++) {
		int flag = 1;
		for (j = 0; j < a; j++) {
			t[i][j] = str[z++];
			if (z == len) {
				flag = 0;
				break;
			}

		}
		if (flag == 0)
			break;

	}
	printf("\n Encrypted as ：\n");
	for (i = 0; i < a; i++) {
		for (j = 0; j < h; j++) {
			if (t[j][i] != '\0') {
				printf("%c", t[j][i]);
			}
		}
	}
	printf("\n");
}
void m() {
	printf("------- The fence is encrypted -------\n");
	printf("-------1, encryption ---------\n");
	printf("-------2, Decrypt ---------\n");
	printf("-------0, Exit procedure -----\n");

}
void decrypt(char str[10000]) {
	printf(" Please enter the string ：\n");
	gets(str);
	int a;
	printf(" Please enter the number of fences :");
	scanf("%d", &a);
	char t[1000][1000];
	int len = strlen(str);
	int i, j;
	int h = len / a, s = len % a;
	int z = 0;
	for (i = 0; i <a; i++) {
		int flag = 1;
			h=len/a;
		
		for (j = 0; j < h; j++) {
			if((i+1)<=len%a)
			    h=len/a+1;
			t[j][i] = str[z++];
			if (z == len) {
				flag = 0;
				break;
			}
		}
	
    if(flag==0)
    break;
	}
  printf("\n  After decryption :\n");
 	h=len/a+1;
  for (i = 0; i <h; i++) {
		for (j = 0; j <a; j++)
    {        if(t[i][j]!='\0')
			printf("%c",t[i][j]);
		}

	    
} printf("\n");
}

Simple RSA

use c Writing explosion longlong 了 , I use... Directly python Write the script

def EnCrypt(m):
    print(" Please enter q,p,e")
    q,p,e=eval(input())
    n=q*p
    c=(m**e)%n
    print(" The secret is :")
    print(c)
def DeCrypt(m):
    print(" Please enter q,p,e")
    q, p, e = eval(input())
    n = q * p
    fn=(q-1)*(p-1)
    d = 2
    while (e*d)%fn!=1:
        d=d+1
    c = (m ** d) % n
    print(" Plaintext is :")
    print(c)
print("rsa")
a = 1
while a:
    print(' Please enter the number to encrypt and decrypt ')
    c = eval(input())
    print(" Encryption select 1, Decryption selection 2,")
    ch = eval(input())
    if ch==1:
        EnCrypt(c)
    elif ch==2 :
        DeCrypt(c)
    else:break

While cleaning up the computer files, I suddenly found this , break out .