From libsrc4/tst_vars.c, the following code demonstrates the use of per variable compression. Use the nc_def_var_deflate function, after a var has been defined, before leaving define mode.
if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR;
if (nc_def_dim(ncid, DIM1_NAME, DIM1_LEN, &dimids[0])) ERR;
if (nc_def_dim(ncid, DIM2_NAME, DIM2_LEN, &dimids[1])) ERR;
if (nc_def_dim(ncid, DIM3_NAME, DIM3_LEN, &dimids[2])) ERR;
if (nc_def_var(ncid, VAR_BYTE_NAME, NC_BYTE, 2, dimids, &byte_varid)) ERR;
if (nc_def_var_deflate(ncid, byte_varid, 0, 1, DEFLATE_LEVEL_4)) ERR;
if (nc_def_var(ncid, VAR_CHAR_NAME, NC_CHAR, 3, dimids, &char_varid)) ERR;
if (nc_def_var_deflate(ncid, byte_varid, 0, 1, DEFLATE_LEVEL_4)) ERR;
if (nc_put_var_schar(ncid, byte_varid, (signed char *)byte_out)) ERR;
if (nc_put_var_text(ncid, char_varid, (char *)char_out)) ERR;
...
/* Open the file and check data. */
if (nc_open(FILE_NAME, 0, &ncid)) ERR;
if (nc_get_var_schar(ncid, byte_varid, (signed char *)byte_in)) ERR;
for (i = 0; i < DIM1_LEN; i++)
for (j = 0; j < DIM2_LEN; j++)
if (byte_in[i][j] != byte_out[i][j]) ERR;