How do you write a C program that interchanges the odd and even elements of an array?

Answer 1

This is easier to achieve using C++ than C, because we can make use a single template function that can cater for arrays of any type in a type-safe manner. In C, we must use macro trickery to cater for different array types, but macros are not type-safe. However, if we limit ourselves to arrays of integers, we can provide a concrete implementation:

void swap_oddeven (int* p, size_t size) {

if (size<2) return;

for (size_t index=1; index<size; index+=2) swap (p[index], p[index-1]);

}

Answer 2

Use the following function:

void exchange_odd_even (int* arr, size_t len) {

for (int i=1; i<len; i=i+2) swap (arr[i-1], arr[i]);

}

Note that we traverse the array from index 1 rather 0, incrementing in steps of 2. This is because index 1 is an even element (the 2nd element) and for every even element in the array we can guarantee there has to be a preceding odd element to swap with. Doing it this way means we don't need to cater for the special case where 'len' is odd and the final odd element has no even element to swap with.