cannot convert parameter 1 from 'char' to 'char *'
calcCharges(type_of_gas, &rate_of_gas, number_of_gallons, &total_gas_of_price, car_wash, &price_of_car_wash, &total_cost);
You don't need to create 3 threads for the same problem. 1 would be enough.
Use &type_of_gas instead of type_of_gas.
Without more code, I cannot help much further.
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