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up vote 1 down vote favorite

i am a beginner in c. i don't know that much how to use arrays as function parameters, arguments or how to return array from an function. to my knowledge, the below code should work fine. But i can't get where the problem is. the function is not working as it should.

//reversing an array using function
#include<stdio.h>
void rev(int array[],int length)
{
    int k,j,temp;
    for(k=length-1,j=0;k>=0&&j<length;k--,j++){
        temp=array[k];
        array[k]=array[j];
        array[j]=temp;
    }
}
int main()
{
    int c,arr[]={1,2,3,4,5,6,7,8,9};
    rev(arr,9);
    for(c=0;c<9;c++){
        printf("%d ",arr[c]);
    }
    return 0;
}
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In fact you can't directly pass an array as a function argument, or return one as a function result. The parameter declaration int array[] really means int *array, a pointer (this applies only to parameter declarations). Suggested reading: section 6 of the comp.lang.c FAQ. –  Keith Thompson Aug 6 '12 at 9:39
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3 Answers

up vote 3 down vote accepted

You only need to go until the middle of the array, if you go more, you re-reverse the array:

So this:

for(k=length-1,j=0;k>=0&&j<length;k--,j++){

Should be:

for(k=length-1,j=0;k > j;k--,j++){
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thanks very much. i just figured myself it just after posting it in the forum. thanks very much. –  Nasif Imtiaz Ohi Aug 6 '12 at 8:48
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up vote 0 down vote

It looks to me like you're performing the reverse twice.

That is, you swap the beginning and end elements immediately, and at the end of your iteration you swap them again. i.e. you end up with the same array.

You can either:

  1. perform your swap only halfway through your array, or
  2. populate a second array in reverse from the first (I don't know if you want to repopulate the original array, however - you may need to copy it back in)
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up vote 0 down vote

There no problem with array. Problem with your algo. //reversing an array using function

#include<stdio.h>
void rev(int array[],int length)
{
    int k,j,temp;
    for(k=length-1,j=0;k>=0 && j<length / 2; k--,j++){
        temp=array[k];
        array[k]=array[j];
        array[j]=temp;
    }
}

This reverse array. Your algo reverse it twice. So just add /2 in for conditions.

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