Need help with a small problem

This is a discussion on Need help with a small problem within the C++ Programming forums, part of the General Programming Boards category; Given the following program : Code: #include <iostream> using namespace std; struct quest { int * ptr; char c; }; ...

  1. #1
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    Question Need help with a small problem

    Given the following program :

    Code:
    #include <iostream>
    using namespace std;
    
    struct quest
    {
      int * ptr;
      char c;
    };
    
    int main()
    {
         quest q;
         *q.ptr = 7;
         q.c = '4';
         return 0;
    }
    I am supposed to fix the error in the program without adding or changing any variable names or data types. The error I get when I run this program is "c4700: uninitialized local variable 'q' used." I think that this is because in the statement "*q.ptr = 7;" 7 is being assigned to the variable pointed to by ptr, but ptr has not been set to point to another variable yet. I thought of declaring another variable and having ptr point to it, but my instructions say to not add any other variables. How do I fix this without changing or adding any variables?

  2. #2
    -bleh-
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    Quote Originally Posted by Freddy92 View Post
    Given the following program :

    Code:
    #include <iostream>
    using namespace std;
    
    struct quest
    {
      int * ptr;
      char c;
    };
    
    int main()
    {
         quest q;
         *q.ptr = 7;
         q.c = '4';
         return 0;
    }
    I am supposed to fix the error in the program without adding or changing any variable names or data types. The error I get when I run this program is "c4700: uninitialized local variable 'q' used." I think that this is because in the statement "*q.ptr = 7;" 7 is being assigned to the variable pointed to by ptr, but ptr has not been set to point to another variable yet. I thought of declaring another variable and having ptr point to it, but my instructions say to not add any other variables. How do I fix this without changing or adding any variables?
    You can use "new" to allocate memory for ptr. then you can store a value at that memory location.

  3. #3
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    19
    Thank you very much.

  4. #4
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    Sorry for the double post, I just have another question and didn't see an edit button.

    I was trying to figure out when it would be legal to use the ++ operator on an array. For instance, if you have:
    Code:
     int arr = {1, 2, 3, 4, 5};
    could the statement arr++ be used to increment the address or something? I'm just trying to figure out exactly what ++ can be used for. Thanks.

  5. #5
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    You can't increment arrays. However, you can increment pointers so they progressively act on elements of an array.

    For example;
    Code:
    #include <iostream>
    int main()
    {
          int arr[] = {1, 2, 3, 4, 5};
    
          int *p = arr;
          int *end = arr + 5;    // as we have 5 elements in array
    
          while (p != end)
          {
               std::cout << *p << '\n';
               ++p;
          }
    }
    will print the elements of your array, one per line.

    Note that end points one past the last element of the array. That means it cannot be dereferenced, but it does provide a marker for ending the loop.
    Right 98% of the time, and don't care about the other 3%.

  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    Don't forget that when using new, you must also use delete.
    As for useful reading, I'd recommend smart pointers. They always go hand-to-hand with new, so it is useful reading and knowledge.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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