Thread: Encoding with random ASCII

I have to creat a program:

1.enter a line of text and convert to ASCII
2.encode the text by adding a random nunber to the ASCII char.


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


unsigned int a[80],ran,n=0,t,len=0,asc[80],n1=0,n2=127;
char input[80],ch;

void main(){

scanf("%s",&input); //receive data input
len=strlen(input)

for(int i=0;i<len;i++){
asc[i]=input[i];
asc[i]+=ran;

}
(then print it by for loop)
}

how can i made a different random no. whenever i run it?
and space can't be converted in ASCII when printing while i input a space in text.

If the problem is generating random numbers, you should look at this simple code:

Code:

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

int num_ran(int max)
{
    int num;

    randomize();
    num = rand() % max;

    return num;

}

int main()
{
    int rand_num;

    rand_num = num_ran(30);
    printf("The random number was: %d\n",rand_num);

    return 0;
}

Actually the procedures are:

1.
Convert each character, including blank space, to its ASCII equivalent

2.
Generate a positive random integer. Add this integer to the ASCII equivalent of each character. The same random integer will be used for the entire line of text.

3

Suppose that N1 represents the lowest permissible value in the ASCII code, and N2 represents the highest permissible value.

If the number obtained in Step 2 above (I.e., the original ASCII equivalent plus the random integer) exceeds N2, then subtract the largest possible multiple of N2 from this number, and add the remainder to N1.

Hence the encoded number will always fall between N1 and N2, and will therefore always represent some ASCII character.

4
Display the characters that correspond to the encoded ASCII values.

5.The procedure is reversed when decoding a line of text. Be certain, however, that the same random number is used in decoding as was used in encoding.

Although it is simply a conversion with addition in no., I am still confused....

Originally posted by moi
problems:

includes conio.h, a nonstandard header, for no good reason.
uses randomize(), a nonstandard function.
uses the "rand() % n" method to generate random numbers in a certain range which can be quite inaccurate

The code can't be run in VC++, it showed a error message:

error C2065: 'randomize' : undeclared identifier

why?

And can I use "time" to generate random numbers?
What's the code?

Originally posted by stevenC
The code can't be run in VC++, it showed a error message:

error C2065: 'randomize' : undeclared identifier

why?

And can I use "time" to generate random numbers?
What's the code?

randomize is a NON standard function like moi said.
You can use time to create pseudo random numbers. Just call srand with time( NULL ) as the parameter and then call rand() and mod it with your limit.

Originally posted by MrWizard
randomize is a NON standard function like moi said.
You can use time to create pseudo random numbers. Just call srand with time( NULL ) as the parameter and then call rand() and mod it with your limit.

I still dont know how to embed it...
Is it correct as follows?There is still error in VC++.
Is there any C program run the following code without errors?

Code:

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


unsigned int a[80],ran,n=0,t,len=0,asc[80],n1=0,n2=127;
char input[80],output[80],ch;




int main(void){
	
/*->*/	srand( (unsigned)time( NULL ) );
	
	printf("This is a text encoding program.\n");
	printf("Please enter text wanted to be encoded.\n");

 /*->*/   ran= srand() ;	//a random no. is generated

	printf("%d\n",ran);
	gets(input); //receive data input
	
	len=strlen(input);	//calculate the length of text inputted

	printf("There are %d characters inputted(include blank space).\n",len);	

	//

	
	for(int i=0;i<len;i++){ 
		asc[i]=input[i];	//convert char to int 1st
		asc[i]+=ran;		//encoding by addition with a random no.
		
		while(asc[i]>n2){//the loop ensure the no. is inbetween ASCII range
			if(asc[i]>=0){
				asc[i]-=n2;	  
				a[i]++;
			}
		}
	
	}

	
	printf("The text is encoded as follows:(include blank space) \n");

	for(int j=0;j<len;j++) printf("%d ",asc[j]);
	//printf("\n%d",ran);
	printf("\n\n");

	printf("Do you want to decode the statement above?(y/n): "); //ask user of decoding
	scanf("%c",&ch);  //receive command
	if((ch=='y')||(ch=='Y')){	//if confirm, start decoding
		for(int u=0;u<len;u++){		//return to original text for each character as follows:
			if (a[u]!=0){
				output[u]=a[u]*n2+asc[u]-ran;	//(for char exceed ASCII before encode)
				
			}
			else
				output[u]=asc[u]-ran;		//(for char inbetween ASCII before encode)
		}
		printf("The original text is:\n");
		for (int k=0;k<len;k++) printf("%c",output[k]);	//print out the original text
		printf("\n");
	}

return 0;
}


error C2065: 'time' : undeclared identifier
error C2660: 'srand' : function does not take 0 parameters

Code tags added by kermi3

Thank you kermi3