rand() generating the same number – even with srand(time(NULL)) in my main!

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The issue is that the random number generator is being seeded with a values that are very close together – each run of the program only changes the return value of time() by a small amount – maybe 1 second, maybe even none! The rather poor standard random number generator then uses these similar seed values to generate apparently identical initial random numbers. Basically, you need a better initial seed generator than time() and a better random number generator than rand().

The actual looping algorithm used is I think lifted from Accelerated C++ and is intended to produce a better spread of numbers over the required range than say using the mod operator would. But it can’t compensate for always being (effectively) given the same seed.

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