There are idioms and methods for writing reliable C programs, which you learn with experience and reading better code than yours. If you learned languages in the order higher-to-lower, you eventually understand that you cannot write a program in C at the same pace as in a higher level language.

What has worked for me is: always have a second terminal open for the manual pages and the standards; and to regularly read quality C source code. Opengroup.org has thorough references for the standard C library, including its relationship to POSIX and the SUS; and the various kernels and core Unix utilities are always a good read.