Adding integers inside of an array

I'm horrible at C and I have to write a program for class that's due tomorrow that has to do with UPC codes. Basically I'm supposed to prompt the user for a 12 digit UPC and then check to see if it's valid or not. To do this I have to store the UPC in an array.

Now, I know how to check if the UPC is valid on paper. You have to add all the odd positions (for example, if the UPC is 268473619543 you would add 2, 8, 7, 6, 9 and 4 together) and then multiply that number by 3. Then I have to add all the even positions in the UPC and add that to the odd position's sum.

Anyway, what my problem is I can't figure out how to do this in code. How would I add the numbers while they are stored into an array?

for(i=0;i<arraysize; i+=2)
sumEven+=array[i];
sumOdd+=array[i+1];

Get one thing to work at a time. first prompt the user and scan in a UPC code. Post some code, It will be easier for people here to help you when you have something down already. What you might want to do it use the UPC code as a string. That way you can traverse through the numbers and add up the odd/even positions individually.

Just for loop like I did to go through every value in the array starting from 0. In this case you want to add every even and odd number. Easiest way is to do i and i+1 to represent even and odd. i+=2 will increment it by 2 every time it goes through loop, then add the values as it goes through to a variable you wish. If it is multi dimensional just nest another for

Sorinx, I think what Randy is trying to do is add up the actual odd/even numbers of the single UPC code, not the array itself.

Wait that works... he just has to store 1 UPC code in a int array...Then add the numbers in the odd positions... i is just the pointer to the address that stores the value that he entered for the UPC code

Yes I have to store 1 UPC code into an array and then add the odd/even positions in the array. Will the for loop work for that?

Yeah man lol, idk what he's talking about. Use for loops to read/store in arrays unless you have predetermined values. Just follow the template I set up

@ Sorinx Post some pseudocode on here and explain to me what you mean. If you enter a UPC code into an array and you use your technique then the UPC array should not be an int array. It should be a string. Unless he is hard coding the int array like such

Code:

---

UPC[]={1,4,7,9,3........};

---

I fail to see how your code will work... Unless the user inputs the UPC number one integer at a time. Randy, are you supposed to enter the UPC code like this 1 enter 4 enter 5 enter..... Or, is it supposed to be one number like 487233455... enter.

Lol or you could take the UPC code from the user 1 value at a time with a scanf in a print statement incrementing the pointer every time a number goes through. Boom done, and quite on the level that he is. No need to get into strings malloc and rewind with a beginner

Sorinx, how would I go about doing that method? Not to be a pain in the ass, but I'm pretty lost here. I've only been working with C for a few weeks now.

Yes, I could see that working. I was assuming that the number was entered like a number should be entered, which is all on one line.

it's cool you have your array size so make a

Code:

---

printf("enter in one number of UPC code hit enter enter in next or whatever you want");
for(i=0;i<12;i++){
scanf("%d\n", &arrayName[i]);}

---

now your compares and ........ will be a lot easier because like you said you are a few weeks in now, it gets a bit complicated lol

dont

Quote:

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Originally Posted by camel-man

Yes, I could see that working. I was assuming that the number was entered like a number should be entered, which is all on one line.

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And you can't figure out how to move the pointer inside the cell? lol I have been only doing C for 3 months...

No, I know how to "move the pointer inside of the cell" just fine :P

Haha well this way would be a lot easier and outside the box for him

Okay this is what I have set up so far

Code:

---

int a[12], i, sumEven, sumOdd, total, entry;
printf("Type in one number of the UPC code and press enter");
for(i=0;i<=12;i++){
scanf("%d\n", &a[i]);}
for(i=0;i<=12; i+=2)
sumEven+=a[i];
sumOdd+=a[i+1];

total = sumOdd*3 + sumEven;

---

Do I have it placed all in the correct order?

Lol hold on I'll fix it up a bit. I didn't try and compile. Make sure you realize that arrays start at value 0. so you doing <=12 isn't going to store 12 values.

Code:

---

#include <stdio.h>

int main()
{
int a[12], i, sumEven, sumOdd, total, entry;
    printf("Type in one number of the UPC code and press enter");
        for(i=0;i<12;i++){
            scanf("%d\n", &a[i]);
                        }
       
       
        for(i=0;i<12; i+=2){
            sumEven+=a[i];
            sumOdd+=a[i+1];
                            }
total = sumOdd*3 + sumEven;

}

---

I hope you understand how this and why it works. For loop sets i to zero then checks if its less than 12. If it's less than 12, it scans the value entered by user into the array at i. then incremements i til i<12 is no longer viable. The second part I incremented by 2 because you wanted to add the even and odd numbers. so a[i]+2 will always be even where as a[i+1] will always be odd and it adds it every increment. make sure to use braces when you are doing for loops you need to localize loops

Haha man you are seriously awesome. I'm sorry for being bothersome I just really want to get this done. Thank you for all the help

Dude no problem, I can't figure out my code right now personally haha, and I knew what it was like trying to do ........ when I started 3 months ago and everyone would give some hard ass answer and it would make your head spin. Figured I'd keep it simple

FYI SumEven and SumOdd should be initialized to 0 in the beginning so you are not left with some outrageously high number.

Yeah good call I am doing 2 things at once

Not to nitpick here but also you want to switch the indexes of sumEven and Sumodd

Code:

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  sumEven+=a[i];//<---- this is first number of array meaning 1 in reality. 1= odd
            sumOdd+=a[i+1];// <--- second number 2= even :D

---

switch to

Code:

---

  sumOdd+=a[i];
            sumEven+=a[i+1];

---

Seems like I should get some sleep missing stupid things

Apparently the 12th digit in the array is not actually supposed to be counted. Is there a simple adjustment I can make so that this is the case with the code that's already written?

lol yeah man just change it to i<11. i is the counter, that's why it's set to i = 0. Then the condition is checked for i<11. Then it does the instructions, then it adds 2 to i, and rechecks the counter. so on and so on. (IDK why it deletes certain words out, the forum that is)

I tried that and had it print out the total for both sumEven and sumOdd and it's still counting the last digit in the array even with this

Code:

---

for(i=0;i<11; i+=2)

---

Post what your actual code looks like now, from that, that isn't possible

Code:

---

#include <stdio.h>
 
int main(void)
{
      int i, sumEven=0, sumOdd=0, total=0;
      char UPC[13];
        printf("Enter in Your UPC code\n");
        scanf("%12s", UPC);

        for(i=0;i<12;i++)
        {
                if(i%2==0)
                sumOdd+=UPC[i]-'0';
                else
                sumEven+=UPC[i]-'0';
        }
   
        total = (sumOdd*3) + sumEven;
        printf("Your total is %d\n", total);

        return 0;
}

---

This is what I was getting at, notice the user friendliness. Here you can just enter in the UPC code like a normal UPC code, rather than the tedious enter after enter.

0 to 11 = 12, 0 to 10 = 11

All I have right now is what you gave me earlier pretty much

Code:

---


#include <stdio.h>
 
int main(void)
{
int a[12], i, sumEven, sumOdd, total;
    printf("Type in one number of the UPC code and press enter");
        for(i=0;i<12;i++){
            scanf("%d\n", &a[i]);
                        }
       
        sumEven = 0;
        sumOdd = 0;
        for(i=0;i<11; i+=2){
            sumOdd+=a[i];
            sumEven+=a[i+1];
                            }
total = sumOdd*3 + sumEven;
printf("odd sum is %d\n", sumOdd);
printf("even sum is %d\n", sumEven);
 printf("total is %d\n", total);

return 0;
}

---

I am using 681131700085 as an example UPC. The even sum should only be 10 but it keeps printing out as 15

Yeah that's fine if you want to do a check to make sure value entered has 12 chars

Camel-man, is that using an array though? That's the only option I have with the assignment

He's using a char array and using a string then modulus

Code:

---

#include <stdio.h>

int main()
{
int a[12], i, sumEven=0, sumOdd=0, total=0;
    printf("Type in one number of the UPC code and press enter");
        for(i=0;i<11;i++){
            scanf("%d\n", &a[i]);
                        }
       
       
        for(i=0;i<10; i+=2){
            sumOdd+=a[i];
            sumEven+=a[i+1];
                            }
total = sumOdd*3 + sumEven;
printf("total: %d", total);
}

---

Yes it is using an array, what does your professor require of you? That it be an integer array, char array, or just an array in general? If so then yes it uses a char array, and should work fine.

In class he was giving us examples with int arrays but the assignment itself just says array and doesn't specify. So I assume it would be fine

Well, if he does not specifically direct what array he wants then, I would imagine this would work.
P.S. If you do not want the last digit to be calculated then just change the i<12 to i<11.

Yeah either way works unless you hit enter before 12 chars need to put a few more lines in there lol

Im assuming the user knows exactly what to enter ;) (which is never the case in reality :D)

This is the last part of the problem. If you guys can help at all you will be my freaking heroes: If the last digit in the total is 0, then the check digit is 0; otherwise subtract the last digit from 10 to calculate the check digit.If the computed check digit matches the twelfth digit of the UPC, the UPC is assumed to be correct; otherwise it is incorrect.

I know I have to use a few if statements but what confuses me is how to actually check a specific number like the last digit in the total or checking to see if it matches the last in the array.

Depends on which way you chose to do it really. Strings have a lot of different functions but if you did it my way you would just have to do Array[11] would be the 12th value... so something like

Code:

---

if (a[11]==0)
checkdigit=0;
else
checkdigit=10-a[11];

if checkdigit==a[11];
printf("UPC is correct");

---

You have to do it with the total though like if the UPC was 681131700085, after calculating the total comes to 85. If the last digit is 0 then that's the check digit but if it's not (which it's not because the last digit is 5) then you subtract the last digit from 10 and that's the check digit. Then after all that you have to see if the check digit is equal to the last digit in the UPC. I just have no idea how to write this in code.

(It's a mandatory class, by the way, otherwise I wouldn't be taking it. I think it's pretty clear that I'm not exactly a master of coding)

OH you know what modulus is man? it takes the number divides it by something then returns the remainder. so... %10 would = 5 just rewrite it the same way I did but instead of the array just set checkdigit=total%10; then do your if statements

What I think everyone here has missed so far is that this:

Code:

---

        for(i=0;i<11; i+=2){
            sumOdd+=a[i];
            sumEven+=a[i+1];
                            }

---

gives exactly the same results as this:

Code:

---

        for(i=0;i<12; i+=2){
            sumOdd+=a[i];
            sumEven+=a[i+1];
                            }

---

Think about the possible values of i inside the loop in each case: 0, 2, 4, 6, 8, 10. In both cases you're adding up 6 "odd" digits and 6 "even" digits.