Chern class of Hopf fibration: $S^1 \hookrightarrow S^3 \xrightarrow{\ p \, } S^2$?

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As definition, the first Chern class is an element in $H^2_{dR}(S^2)$, how can we represent it as an integer? If we change the orientation of $S^2$, then does the integer change sign?