For example, some time ago, Switzerland bought unlimited foreign exchange to curb the appreciation of the Swiss franc. What shall we do? Because the Swiss franc is the world currency, and its exchange rate is determined by the market supply. So the SNB's method is to buy foreign exchange indefinitely. As a result, the Swiss franc has increased in the market, while the foreign exchange has decreased, so the Swiss franc has become worthless, and a package of foreign exchange has become more valuable, which directly leads to the depreciation of the Swiss franc and the reduction of the exchange rate.
For all other currencies in circulation, the exchange rate is determined by this supply and demand mechanism (note: RMB is not a currency in circulation). There is no need to calculate, it is completely determined by buying and selling (even if the central bank intervenes, the market mechanism will play a role). As for whether it can increase 100 times, yes, by issuing a new set of currencies and stipulating that the ratio of the existing RMB to the new currency is 100: 1, then your 100 yuan will become 1 yuan. However, the purchase value has not changed, because the new 1 yuan and the old 100 yuan have the same amount of dollars and things to buy ... just the difference in number. According to my current economic knowledge, the nominal exchange rate is the ratio of the price levels of two countries we see multiplied by the real exchange rate. For example, the theoretical exchange rate of RMB against the US dollar should be more than three dollars, but the current exchange rate is more than six dollars, which is related to the government's monetary policy. The real exchange rate should be determined by the actual purchasing power.