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dynamic array

Posted on 2002-07-15
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How to create a dynamic array, with the array size is determine by user input?
Pls give a simple example.Thanx you.
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Question by:exiang
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9 Comments
 
LVL 84

Accepted Solution

by:
ozo earned 100 total points
ID: 7156178
#include <stdio.h>
main(){
    int arraysize;
    int *array;
    int i;
    scanf("%d",&arraysize);
    array = (int *)malloc(sizeof(*array)*arraysize);
    for( i=0; i<arraysize; i++ ){
          scanf("%d",&array[i]);
    }
    for( i=0; i<arraysize; i++ ){
          printf("%d\n",array[i]);
    }
}
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LVL 3

Expert Comment

by:cincin77
ID: 7158967
int he malloc line;
instead of using sizeof(* array) you should use sizeof(int)
as the elements of the array are integers. However for this specifiz example, sizeof(* array) should be equal to 4 which is equal to sizeo(int) :))

regards...
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Expert Comment

by:Theril
ID: 7159913
> instead of using sizeof(* array) you should use sizeof(int)
as the elements of the array are integers. However for this specifiz example, sizeof(* array) should be equal to 4 which is equal to sizeo(int) :))

No, *array points to an int, so the effect is exactly same as sizeof(int). You propably mixed it with sizeof(array)?
Using *array insteads of *int is propably wiser, as there may come situation where one changes the datatype of array.
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LVL 3

Expert Comment

by:cincin77
ID: 7160328
array itself is a pointer and * array is a pointer to a pointer whose size is machine dependent.

do i miss something?
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Expert Comment

by:Theril
ID: 7160963
> array itself is a pointer and * array is a pointer to a pointer whose size is machine dependent.

Maybe I said "*array points to an int" a bit wrong. What I ment was "*array is an int". Elements of int array are ints and *array is first element of the array (array[0]), so it's size is sizeof(int).

Try this one:

#include <stdio.h>
int main()
{
     char *foo = "foo";
     printf("Sizes: foo: %i *foo: %i\n", sizeof(foo), sizeof(*foo));
}
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LVL 3

Expert Comment

by:cincin77
ID: 7161371
iygggg
what i said was really ridiculous, i wrote as if array is a type.
sorry for this mistake.

thanks theril...

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LVL 2

Expert Comment

by:jonnin
ID: 7161859
note that you can resize the array with realloc; this is slow (do not add one element at a time, add 100 or 1000 or something each time you run out of space)

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Author Comment

by:exiang
ID: 7170987
should include a header file called <alloc.h>
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LVL 84

Expert Comment

by:ozo
ID: 7171022
<alloc.h> is not ANSI standard
should include a header file called <stdlib.h>
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