Why this dosen't work in C

This is a discussion on Why this dosen't work in C within the C++ Programming forums, part of the General Programming Boards category; Following code can't be compiled as a C program & but when compiled as C++ program it works. I am ...

  1. #1
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    Why this dosen't work in C

    Following code can't be compiled as a C program & but when compiled as C++ program it works.

    I am experienced with C but quite to new to C++ & OOP, so please explain if you have some time.

    int *SomeArray=NULL,n;
    printf("Enter the number of elements in array : ");
    scanf("%d",&n);
    SomeArray = new int(n);

  2. #2
    (?<!re)tired Mario F.'s Avatar
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    new is a c++ keyword.

    EDIT:
    Also... don't do this:

    int *SomeArray=NULL,n;

    do this:

    int *SomeArray=NULL;
    int n;

    Anyone reading your code will thank you later on. And you will thank yourself too.
    Last edited by Mario F.; 08-31-2006 at 07:48 AM.
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  3. #3
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    Yer, in C you gotta replace new with something like malloc() for dynamic memory.

  4. #4
    The superhaterodyne twomers's Avatar
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    >> int *SomeArray=NULL,n;

    >> int *SomeArray=NULL;
    >> int n;

    I can see why Mario suggested you put it on different lines, but there isn't really a need. It's more for the sake of readability than anything. It's just that the pointer (*) indicator of SomeArray doesn't carry through to n, as I think you know. So, to distinguish between pointers, and non-pointers easily, new lines are often used.



    EDIT ::

    A more C++-ish implementation of your code Not color coded unfortunately

    Code:
    #include <iostream>
    
    using namespace std;
    
    int main( void )
    {
        int *SomeArray = NULL;
        int n = 0;
    
        cout<< "Enter the number of elements in the array: ";
        cin >> n
    
        SomeArray = new int[n];
    
        // Do stuff with the array
    
        delete []SomeArray;
    
        return 0;
    }
    Last edited by twomers; 08-31-2006 at 08:05 AM.

  5. #5
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    Thank you.

    Thank You, for giving C++ code.

    I tried to do following & compiled as C program but I am getting errors

    code> SomeArray = realloc(SomeArray,n);
    error> invalid conversion from `void*' to `int*'

    I get similar error if I do it using malloc

    (I use DevC++ IDE which uses gcc compiler)

    I googled but, everything I find is giving some errors, Anyone knows how to do it in C, or may be I should post it in C board ?
    Last edited by ruab; 08-31-2006 at 09:45 AM.

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    You're using a C++ compiler to compile C code. Save the file as a .c file. If that still doesn't work, you may have to cast the *alloc call. BTW, realloc doesn't do what you want. Try malloc().
    Code:
    SomeArray = malloc(sizeof(int) * n);
    dwk

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  7. #7
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    malloc error

    I tried
    Code:
    SomeArray = malloc(sizeof(int) * n);
    but it's giving same error as above. When it's saved with .c extension.

  8. #8
    Frequently Quite Prolix dwks's Avatar
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    SomeArray has to be a pointer, not an array.

    Try including <stdlib.h>.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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  9. #9
    and the hat of wrongness Salem's Avatar
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    Are you sure it's the same error, and not int to int* ?
    Did you include stdlib.h ?
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  10. #10
    Code Goddess Prelude's Avatar
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    >but it's giving same error as above. When it's saved with .c extension.
    If you're getting the same pointer conversion error then you're still compiling as C++. C allows conversions to and from void*, but C++ requires a cast when converting from void*.
    My best code is written with the delete key.

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