how to rectify this error and make the code work?

i am facing problem in the decryption code , however encryption code is working correctly. the error coming is : ??? Index exceeds matrix dimensions.

Error in ==> Decrypt_text at 15 while(im(x,y)~=0)&(x<q)&(y<p)

Answer 1

[Joseph Cheng]

for the error "index exceeds matrix dimensions" it is far simpler for you to debug it and learn from it. All you need to do is just put a debug breakpoint at that spot or a try-catch debug code to catch the error at which iteration.

Without digging all your code I can venture a guess just by looking at the error line. I am pretty certain you're incrementing x and y in the loop. And at some point you're doing x= x+1 or y = y+1 one too many times such that it no longer within the dimensions of im(). So to correct this your while conditional statement should be adjusted or pick when you're incrementing x or y such that you don't exceed dimensions of im().

Answer 2

[Geoff Hayes]

Anushree - since your p and q are determined by

 [p,q,r]=size(I'm);

and your conditions for the while loop are

 im(x,y)~=0&(x<q)&(y<p)

change the order of the conditions so that you check whether x and y are less than the number of rows and columns of im before you try to use them as indices into im. Try using

 while x<=q && y<=p && im(x,y)~=0

Note that I've changed the conditions to allow for equality (maybe this isn't correct for your tests but they are still valid indices for im) and that I've replaced the & with && because it exhibits the short circuiting behaviour that the single ampersand does not.

[Anushree Bhatt]

now there is no error but the code is not giving the desired output. i had entered the string 'hello' , on decryption i am supposed to get the value of 'hello' back at str . Instead i am getting a very weird value :

T,V.$.ze: N6MB`2F,

this is the value.

[Anushree Bhatt]

i tried a different thing .I changed the contents of the entire while loop. the following attached is the new code for decryption but it is not giving the desired output.