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This looks like just a warning; it shouldn't prevent your code from compiling and running.

The warning in question is telling you that you're asking it to print an unsigned type with a signed format string:

warning: format ‘%d’ expects argument of type ‘int’, but argument 8 has type ‘std::queue<int>::size_type {aka long unsigned int}’

Instead of using the %d type specifier, you should use an unsigned specifier like %ud, or the dedicated specifier for size_t: %zd