Write a program to copy the contents of one array into another in the reverse order?

Answer 1

do something like this

char[] myArr = {'a','b'};

StringBuilder sb = new StringBuilder();

sb.reverse();

char[] charArr = sb.toString().toCharArray();

or something like this

char[] charArr = new char[myarr.length];

for (int i=myarr.length-1,j=0;i>=0;i++,j++){

charArr[j] = myarr[i];

}

Answer 2

When copying a sequence of elements, we need to know three pieces of information: where the sequence begins, where it ends and where to place the copies. To define a range within an array we typically specify the start address and the count of elements in the sequence. This creates a half-closed range because, in a given range of n elements starting at address a, the address a+n is one-past-the-end of the sequence. This is important to remember because, if we want to reverse the sequence, the sequence will be off-by-one.

In C, we can efficiently reverse an array with the following function:

void reverse (int src[], unsigned size, int dst[]) {

int* p = src + size;

while (p != src) *dst++ = *--p;

}

Note that dst must be at least as long as size. We do not test for this as there's no way to test that src is at least as long as size, let alone if dst is. So there's no point in even trying; error-checking is the responsibility of the caller. If you need range-checked arrays then C is not the language for you.