Multiplying large numbers in divide and conquer method C++

What you are looking for is a "bignum" library (for integers) or a high-precision floating point library.

Just search for these terms. But you might not found one that works out-of-the-box with the old Turbo-C++ compiler. So you have to the build the library from the sources and apply modifications for the Turbo-C++ compiler if necessary.

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Multiplying large numbers in divide and conquer method

As far as I understand your question, there is no "divide and conquer method" to multiply 2 large numbers. Details may vary, but there is basically 1 method.

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Other friends say to me it solved with arrays

An array is the way to store slices of a very large number, but you have to devise the way to store, retrieve and do the multiplication.
Libraries exist that can handle such numbers, it is named BigInt.
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