Can write C language into Quartus II

In Quartus as such Hardware Description Languages such as Verilog or VHDL are used. But Altera provides a nice environment for developing embedded systems that can be progammed by means of C. This is done in the Nios-II processor. Along with Nios-II you have a complete suite of tools by which you can IP-blocks and periferals. This can be done in the Qsys environment. (formerly SOPC).