| calendar | |
| car | |
| cdr | |
| chebyshev | cheby1, cheby2, cheby_deriv, cheby_eval, cheby_fit, cheby_integ, fil_cheby1, fil_cheby2 |
| chi-square | gammp, gammq |
| close | close at_pdb_open, close, close102, fits, font, h_close, hcp_finish, mpeg_close, mpeg_create, mpeg_write, multif, multio, silo_close, slice2_precision |
| color | color brighten, color, color_bar, edges, eps, epsi, hollow, lightwf, mspace, palette, pdf, pl3surf, pl3tree, plc, plf, plfp, pli, plmk, plwf, pnm_write, rez_kstyle, rezone, slice3, split_bytscl, window |
| complex | conj, fft, fil_analyze, fil_make, fil_response, fits, fits_parse, idl_open, im_part, install_struct, laguerre, roll, sign, strfind, ylm_coef |
| condition number | LUrcond, merge |
| conjugate | conj, fil_make |
| contour | contour contour, get_style, plc, plc_label, plfc, plq, triangle |
| convolution | convol |
| copyright | copyright copyright, warranty |
| cos | cos |
| cosine | acos, internal_rays |
| cray | cray_primitives, createb |
| cubic spline | spline, sprime, tspline |