Problem in simple code.

Hi,
I am having a problem with this seemingly simple code. This is a program that I'm writing from a book. It asks the user to enter a zip code. If the zip code is already in the zip code array, it should increment the corresponding counter in another array. If it is not in the zip code array, add it to the END of the array and increment the counter. Then it displays the contents of the two arrays: the zip codes and the number of times each appeared.

Because the zip codes have to be added to the end of the array, the first for loop starts with the highest number and decends to the lowest. The problem seems to be that although the codes are entered from the last to the first element of the array, they are displayed from first to last. This causes the program to display 0's or just garbage values for the first elements of both arrays. If I change the display loops to display in reverse there is no problem. Any help would be appreciated. (BTW, cant use zips starting with 0.)

Code:

---

#include <stdio.h>

#define num_of_codes 5
#define num_of_counters 5

main()

{
        int zip_codes[] = {0,0,0,0,0},
                counters[] = {0,0,0,0,0},
       
                codes,                                               
                response=1,                                       
                entered_code;


        while(response)

        {

                printf("\nPlease enter a zip code: ");
                scanf("%d" , &entered_code);

               
                for(codes=num_of_codes; codes>0; --codes)
               
                        if(zip_codes[codes] == entered_code)
                                ++counters[codes];
               
                       
                        else
                                                                                                                                                               
                                if(zip_codes[codes] == 0)
                                        {
                                                zip_codes[codes] = entered_code;
                                                ++counters[codes];
                                        }
                                       
                                       
                                               
               
                        printf("\nwould you like to process another?(1 for yes, 0 for no): ");
                        scanf("%d" , &response);

        }
                       
       
        for(codes=0; codes<5; ++codes)
                printf("%7d" , zip_codes[codes]);
                       
                printf("\n");
                               
        for(codes=0; codes<5; ++codes)
                printf("%7d" , counters[codes]);

            printf("\n");
                               
}

---

If I change the last two for loops to the values of the first:

Code:

---

for(codes=num_of_codes; codes>0; --codes)

---

everything works.

Code:

---

for(codes=num_of_codes; codes>0; --codes)
               
                        if(zip_codes[codes] == entered_code)
                                ++counters[codes];
               
                       
                        else
                                                                                                                                                               
                                if(zip_codes[codes] == 0)
                                        {
                                                zip_codes[codes] = entered_code;
                                                ++counters[codes];
                                        }
                                       
                                       
                                               
               
                        printf("\nwould you like to process another?(1 for yes, 0 for no): ");
                        scanf("%d" , &response);

---

u need to realize that the this bit of code will be executed 5 times for every response,that means that every 0 in the zip[codes] array will be replaced by what the user enters the first time,so after that no matter what the user enters it wont go into zipcodes array.

lol sorry. The prompt should be inside the loop:

Code:

---

for(codes=num_of_codes; codes>0; --codes)
                {       
               
                        printf("\nPlease enter a zip code: ");
                        scanf("%d" , &entered_code);

                       
                        if(zip_codes[codes] == entered_code)
                                ++counters[codes];
               
                       
                        else
                                                                                                                                                                /*for(codes=num_of_codes; codes>0; --codes)*/
                                if(zip_codes[codes] == 0)
                                        {
                                                zip_codes[codes] = entered_code;
                                                ++counters[codes];
                                        }
                                       
                }

---

But even so, it doesn't work right:

Code:

---

Please enter a zip code: 12345

Please enter a zip code: 54321

Please enter a zip code: 98745

Please enter a zip code: 45789

Please enter a zip code: 66354
      0  66354  45789  98745  54321
      0      1      1      1      1

---

The first entry 12345 should be the last one in the output, and the first element in both arrays are 0. :confused:

This for loop is wrong:

Code:

---

                for(codes=num_of_codes; codes>0; --codes)

---

That results in a buffer overflow. The first value of "codes" within the loop is 5, and the last value is 1. But arrays go from 0 to 4!
That loop would need to read:

Code:

---

                for(codes=num_of_codes-1; codes>=0; --codes)

---

The "increment" part of the for loop syntax is always run AFTER each iteration. Your later two for-loops are correct, although they should use the #defines defined earlier, instead of just having "5" hard-coded in them. While I'm on the subject, you're #defines should be uppercase too.

Thanks folks,
If you cant tell I'm fairly new at this. Arrays sometimes throw me because of the offset thing. Have to pay more attention. :p

Quote:

---

Originally Posted by qqqqxxxx

and for checking u need to have nested loops.

---

what did you mean by "checking"?

>and for checking u need to have nested loops.
if your code is working the way u want it to,that doesnt matter then.