Re-arrange the odd/even to odd/even places

Given an array of integers [3,1,4,5,7,6,10,8],
re arrange elements such that either even numbers in even locations or odd numbers in odd locations.
in O(n)

output :  6 1 4 5 8 3 10 7

#include<stdio.h>

void Swap (int A[], int i, int j)
{
    int temp = A[i];
    A[i]=A[j];
    A[j]=temp;
}

int main()
{
    int A[] = {3,1,4,5,7,6,10,8};
    int i=0,j=1,n;
    n=sizeof(A)/sizeof(int);
    while(i<n)
    {
        while(i<n && A[i]%2 == 0)
            i+=2;
        while(j<n && A[j]%2 == 1)
            j+=2;
        if(i<n && j<n)
            Swap(A,i,j);
    }// end of while

    for(i=0;i<n;i++)
        printf(" %d",A[i]);

return 0;
}

Let me know your thoughts

WAP to return numbered index if input is excel sheet column header name. e.g excel sheet column headers are A, B, C , D ... Z, AA, AB...AZ, BA,, etc if Input is D , output should be 4 and for AA output should be 27

INPUT                 OUTPUT

A                          1   

AA                        27   

BA                        53   

AAA                      703  



//    TIME : O(n)

#include<stdio.h>
#include<string.h>
int main()
{
    int i=0,l,x,index=0;
    char S[5];
    printf("Enter Column header : ");
    gets(S);
    l=strlen(S);
    while(i<l)
    {
        x=S[i++]-'A'+1;
        index=index*26+x;
    }
    printf("%d",index);
return 0;
}