Input to array loops forever [C]

This is a discussion on Input to array loops forever [C] within the C Programming forums, part of the General Programming Boards category; Alright I'm tackling an assignment and I just started with the input of numbers into an array. It seems to ...

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    Registered User Quixiotic's Avatar
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    Input to array loops forever [C]

    Alright I'm tackling an assignment and I just started with the input of numbers into an array. It seems to be working well, but what happens is once the for loop should be over, it repeats but not at zero like it should (If I wanted it to, which I don't). I'm confused so here's my code:
    Code:
    #include <stdio.h>
    
    
    #define ARRSIZE 19
    
    
    int main(){
    
    
     int temp[ARRSIZE];
     int press[ARRSIZE];
     int i;
    
    
     printf("\n--------------------------------------------------\n");
     printf("  Please enter a temperature and a pressure value.\n");
     for(i = 0; i <= ARRSIZE; i++){
       printf("%d: ", i+1);
       scanf("%d %d", &temp[i], &press[i]);
       } /* for() filling arrays with input */
    
    
     printf("Thank you!");
    return 0;
    } /* main() */
    When it starts the next iteration it starts with i=2 which I'm confused about only slightly less than why it's even looping again in the first place.

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    The code below results in undefined/unallocated space being used.

    Code:
    for(i = 0; i <= ARRSIZE; i++){
    change to the use of "<=" should be "<".

    Code:
    for(i = 0; i < ARRSIZE; i++){
    The location temp[ARRSIZE] is NOT in temp!

    Tim S.

  3. #3
    and the hat of wrongness Salem's Avatar
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    > for(i = 0; i <= ARRSIZE; i++)
    I don't know about the start, but on the last iteration of this loop, you're stepping off the ends of the arrays (and possibly trampling all over your subscript).

    At which point, all bets are off.

    Use <ARRSIZE, not <=ARRSIZE
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    Registered User Quixiotic's Avatar
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    Well thank you all so much, sure did fix the issue. So just that I have a better understanding of the issue, is the final iteration when it reaches 19 that it's going out of the range?

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    Arrays start at zero an stop at SIZE - 1. So in your case 0 - 18.

    Jim

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    Quote Originally Posted by Quixiotic View Post
    Well thank you all so much, sure did fix the issue. So just that I have a better understanding of the issue, is the final iteration when it reaches 19 that it's going out of the range?
    A common error for people to make is confusing "the number of elements" with "the number of the element".

    This is because we humans mostly start counting at 1... C starts at 0.

    As Jim explains if you have a 10 element array you have valid subscripts 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 ... it's ok, count them, there are 10.

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