Question

Write a C program that prompts the user to enter a series of integers that represent a coded message. I have given you the decoder program so that you can see how it is written using array notation. Your assignment is to convert the code to a program that uses only pointers and pointer math.

Your program must use pointer notation and pointer math (i.e. no array index notation other than in the declaration section, no arrays of pointers and no pointer offsets).

The dialog with the user might look like:

Enter string digits to decode:

109 138 145 145 148 81 69 142 153 76 152 69 146 138 70 10

Enter the secret offset integer: 37

Decoded:

Hello, it's me!

Note: The blue text represents the "user input" from your program and is shown for clarity only here. It is not required that your output be in this color. (Do not even attempt to try!). Also note that what the user types in is indicated by the bolded black text above. Again, for clarity only. (The text will limited to an 80 character message. To test, copy and paste the entire line of digits above).

Really BIG hint:

You can click on the "decode_arrays.c" link which provides a solution to the program using "array" notation. You should use it as a guide and just modify the code to use pointer notation.

Note: An arrow line comment (< ----) can be found on the code that needs to be removed and replaced by pointer notation.

Answer 1

Note: you have not provide the code but I have written the completely working code.

Code :

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

//decoding is just subtracting offset from given number
char decode(int number,int offset)
{
   return number-offset;//returning decoded value
}

int main(int argc, char *argv[])
{
   //declaring variable
   //also declaring array here
   int i=0,size,arr[10000],offset,temp2;
char temp;
  
   //prompting for input
   printf("Enter string digits to decode:");
//take input until enter is pressed
   do{
scanf("%d%c", (arr+i), &temp); //(arr+i) is same as &arr[i], temp to store space or enter
i++; //increase i to get count
} while(temp!= '\n');//if temp is new line then break
   //prompting for offset
   printf("Enter the secret offset integer:");
   scanf("%d",&offset);

   //printing results
   printf("Decoded:\n");
   for(temp=0;temp<i;temp++){
       temp2=*(arr+temp); //only pointer is used to get array value
       printf("%c",decode(temp2,offset)); //calling decode to get char...remember char and int is same
   }

   getch();//just to hold screen. remove this and conio if you dont need this
}

Output: