Gcc compiler commands and options

I am learning C language and I use code::blocks IDE to write and build C programs. It uses GNU C compiler. I learnt that there are many ways to optimize the code by tweaking the compiler settings and using compilers command. I can see many options to change compiler's setting from the menu. But I don't know how and where开发者_StackOverflow社区 to apply the compilers commands? Any help is appreciated..

Under the Settings menu, select Compiler and Debugger. Select GNU GCC Compiler at the top. Go to the Compiler Settings tab, and within that select the Compiler Flags tab. Scroll about halfway down, and you'll find all of the "-O" related options.