Thread: Stuck on trying to code Ceasar Cipher

Hi all!
I'm trying to do ceasar cipher from a python code. My problem is, I don't know why my C code doesn't work and I need proper guidance. Below is the code for C, the loops work but the if statement seem to be set to false for each iteration. If i but an else statement like printf("fail"), the else is executed and "Fail" is output on the screen each time it loops.

Code:

void crypter(){
    char alphabet[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    char alphabetcap[26] = {'A','B','C','D','E','F','G','H','I','G','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
    int cle,i = 0, j;
    int temp1;
    char newTexte, temp;
    char texte[1000];
    FILE *fp;
    printf("Insert a number: ");
    scanf("%d", &cle);
    printf("Insert a text: ");
    scanf("%c",&temp);
  fgets(texte,1000,stdin);


    for (i; texte != '\0' ; i++)
    {
        for (j = 0; j < 26; j++)
        {
            if (texte[i] == alphabet[j])
            {
                temp1 = (j + cle) % 26;
                newTexte += alphabet[temp1];
            }
        }
    }
    memset(texte,0,strlen(texte));
    texte[1000] = newTexte;
    fp = fopen("foo.txt", "w");
    fwrite(&texte, sizeof(texte), 1, fp);
    fclose(fp);
}

Here the code of python i'm trying to convert into C.

Code:

alphabet = 'abcdefghijklmnopqrstuvwxyz'key = 3
newMessage = ''
message = input('Please enter a message: ')
for character in message:
    if character in alphabet:
        position = alphabet.find(character)
        newPosition = (position + key) % 26
        newCharacter = alphabet[newPosition]
        newMessage += newCharacter
    else:
        newMessage += character
print(newMessage)

Originally Posted by Salem

> newTexte += alphabet[temp1];
C doesn't have the ability to build up a string from a set of characters through addition.

Code:

  printf("%c\n", 'A' + '$' );

This will print 'e', not "A$".

make newTexte an array and write each new character to a subscript of that array.

Thanks for the help i did correct this part. The error i'm getting now is, when I decrypt it, I get special characters instead of letters.

Let say i input aaaa bbbb cccc with a cle = 1, the output should be bbbb cccc dddd, it move each letter by one place as the cle(key) is 1.

Code:

#include <stdio.h>#include <stdlib.h>
#include <string.h>


void crypter();
void decrypter();


int main()
{
	int choix;
	do
	{
		printf("Bienvenue\n");
		printf("Appuyez sur 1 pour crypter un fichier\n");
		printf("Appuyez sur 2 pour decrypter un fichier\n");
		scanf("%d", &choix);
		switch(choix)
		{
			case 1: crypter();
			break;
			case 2: decrypter();
			break;
			default: printf("Erreur le programme va s'arreter");
			break;
		}
	} while(choix != 3);
	return 0;
}


void crypter()
{
	char alphabet[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
	char alphabetcap[26] = {'A','B','C','D','E','F','G','H','I','G','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
	int cle,i = 0, j;
	char temp1;
	char temp,newTexte[1000];
	char texte[1000];
	FILE *fp;
	memset(newTexte,0,strlen(newTexte));
	printf("Inserez un nombre: ");
	scanf("%d", &cle);
	printf("Inserez un texte: ");
	scanf("%c",&temp);
  fgets(texte,1000,stdin);


	for (i; i < 1000 ; i++)
	{
		for (j = 0; j < 26; j++)
		{
			if (texte[i] == alphabet[j])
			{
				temp1 = texte[i] + j;
				newTexte[i] = temp1;
			}
		}
		texte[i] = newTexte[i];
	}
	fp = fopen("test.txt", "w");
	fwrite(&texte, sizeof(texte), 1, fp);
	fclose(fp);
}
void decrypter()
{
	char alphabet[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
	char alphabetcap[26] = {'A','B','C','D','E','F','G','H','I','G','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
	int i, j, cle;
	char texte[1000],ch, temp;
	char newTexte[1000];
	FILE *fp;
	fp = fopen("test.txt", "r");
	printf("Inserez un nombre: ");
	scanf("%d", &cle);
	while (fgets(texte, sizeof(texte), fp)!=NULL)
	{
		for (i = 0; i < 1000 ; i++)
		{
			ch = texte[i];
			for(j = 0; j < 26; j++)
			{
				if (ch == alphabet[j])
				{
					temp = (j - cle);
					texte[i] = temp;
				}
			}
		}
		printf("%c", texte);
	}
}

thanks for taking your time to help, sorry for having disturb, i will restart from scratch for this program