Q.Evaluate $[3.5]$, $[-2.3]$, $[7]$ and $[-7]$, where $[\,\cdot\,]$ denotes the greatest integer function.

These three standard real functions are each defined piecewise rather than by one algebraic expression. The modulus function $f(x)=|x|$ gives the non-negative magnitude of $x$ (domain $\mathbb{R}$, range $[0,\infty)$) and its graph is a V-shaped pair of $45°$ rays meeting at the origin. The signum function reduces $x$ to just its sign, $1$, $0$ or $-1$ (domain $\mathbb{R}$, range $\{-1,0,1\}$), graphed as three disconnected horizontal pieces. The greatest integer function $[x]$ gives the greatest integer not exceeding $x$ (domain $\mathbb{R}$, range $\mathbb{Z}$), graphed as an ascending staircase of unit-wide steps, each closed on its left and open on its right.