void curve (x, y, npts, sym) CURVES.C Level 3
 
float *x  The x vector to be plotted.
float *y  The y vector to be plotted
int npts  The dimension of x and y.
int sym  = 0 draw curve only.
> 0 draw curve and symbols every sym points.
< 0 draw symbols only every sym points.
 
Each time curve() is called, a curve is drawn on the plot in the current color. Sixteen different symbols can be used as curve markers, and nine different line styles are available. The line and symbol styles can be changed automatically by using the legend feature or manually by calling the appropriate routine. curve() is used for any of the linear or logarithmic plots.

Scatter plots may be drawn by calling scatplot(1) before calling curve(). You can still draw symbols every sym 
points.