How does inflation affect GDP?

Inflation is the primary and negative factor of all economic troubles including GDP,
because it lowers consumerism, promote unemployment, and reduce import and export.

-- Not quite. Inflation itself isn't necessarily a bad thing, and in fact deflation (negative price growth) can adversely affect the economy is well. High inflation can certainly hurt spending and employment, but inflation is just a term used for the growth rate of prices, which happens naturally as economies expand. The US Federal Reserve targets an inflation rate of 2-3% as a goal. Inflation has historically been a major concern in some of the developing world especially, and source of economic (and political) instability. (Source: Economics PhD student who just finished grading a paper that cited the above answer)