Thread: Trying to send string to a function and return it back.

One of the problems is that decryptedword is a single character and you are trying to return a char pointer. Second I'm not sure what your trying to do with this line:

Code:

offset = 'word[i]'- 'A';

But surrounding word[i] with single quotes is incorrect for any use. Single quotes signify a character constant, and character constants can only have one char.


Jim

Ok, i updated my code. no errors but warnings. and not getting the right result also.

Code:

#include <stdio.h>
#include <string.h>
char* shift(char *word, int key);
int main()
{
    char word[3]="abc";


    printf("\nThe key move is: %s\n", shift(word, 3));
    return 0;
}


char *shift(char *word, int key)
{
    int i,n;
    int offset;
    char decryptedLetter;
    char decryptedword [3]= {};
    for (i=0;i<strlen(word);i++)
    {
       offset = word[i]- 'A';  
       offset = (offset + key) % 26;
       decryptedLetter = 'A' + offset;
       for (n=0; n<=i; n++)
       {
          decryptedword[n]=decryptedLetter;
       }
    }
    return decryptedword;
}

Warnings

text.c: In function âshiftâ:
text.c:19:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
text.c:29:5: warning: function returns address of local variable [enabled by default]

>a.out

The key move is: P~
·¿ân·àÄ·à
d ô¿·>
à
@ Km·Ã·ô¿·Lm·
ôabc

I have no idea what happend

Any one>? please...

text.c:29:5: warning: function returns address of local variable [enabled by default]

You can't return a local array from your function. I recommend you use the parameter, change the values of the characters and then return that string.

Also this line doesn't allow enough characters for the string:

Code:

char word[3]="abc";

You need to leave room for the end of string character.

Jim

I think when you call your function and it returns the pointer it is going out of scope because the string is only declared locally in the function. so here is what i got

Code:

	
PHP Code:
	

#include "stdafx.h"

#include <stdio.h>
#include <string.h>
char* shift(char *word, int key);
    char decryptedword [4]= {};
int main()
{
    char word[4]="abc";
 
 
    printf("\nThe key move is: %s\n", shift(word, 3));

    char c = getchar();
    return 0;
}
 
 
char *shift(char *word, int key)
{
    int i,n;
    int offset;
    char decryptedLetter;
    for (i=0;i<strlen(word);i++)
    {
       offset = word[i]- 'A';  
       offset = (offset + key) % 26;
       decryptedLetter = 'A' + offset;
       for (n=0; n<=i; n++)
       {
          decryptedword[n]=decryptedLetter;

       }
    }
    decryptedword[strlen(word)] = '\0';
    return decryptedword;
} 

Please avoid the use of a global variable, this is probably not what your instructor is trying to teach you.

Jim

ya just add another parameter in your function so u can pass the address to the local scope of your function your calling and than write the data to a buffer.

like this for example.

Code:

char *shift(char *source, int key, char * destination)

Thanks for the Help!

I am able to do it now.

My next task, is to calculate "letter frequencies" from an array.
ok, I have two arrays, one with words and the other with the letter frequencies.
the words array contains the ciphertext lets say "QXPQB", the letter frequencies array contains freqs. 0.08167, 0.01492... and so on.

basically the array letter frequencies has 26 freqs, each one corresponds to the english letter.

A is 0.08167, B is 0.01492, C is...

Here is what i need to do.

If ciphertext = QXPQB:


Shift of 1 gives RYQRC.


Calculate (freq of R) x (freq of Y) x (freq of Q) x (freq of R) x (freq of C)
= 0.05987 x 0.01974 x 0.00095 x 0.05987 x 0.02782
= 1.9 x 10-9

How would i start this. should I

Code:

// The sample string is "ABC"

int A=0, int B=1, int C=2, int D=3, int E=4; // and so on
// Then maybe text[1]=B so B will int 1^in the above declaration letterfreq[B]=0.01492

freqValue = letterfreq[text[1]] ;

Will that work, or is there an easier way?