The debugging skill of the programmer is probably the biggest factor in the ability to debug a problem, but the difficulty of software debugging varies greatly with the programming language used and the available tools, such as debuggers. Debuggers are software tools which enable the programmer to monitor the execution of a program, stop it, re-start it, set breakpoints, change values in memory and even, in some cases, go back in time. The term debugger can also refer to the person who is doing the debugging.
Generally, high-level programming languages, such as Java, make debugging easier, because they have features such as exception handling that make real sources of erratic behaviour easier to spot. In lower-level programming languages such as C or assembly, bugs may cause silent problems such as memory corruption, and it is often difficult to see where the initial problem happened. In those cases, memory debugger tools may be needed.
In certain situations, general purpose software tools that are language specific in nature can be very useful. These take the form of static code analysis tools. These tools look for a very specific set of known problems, some common and some rare, within the source code. All such issues detected by these tools would rarely be picked up by a compiler or interpreter, thus they are not syntax checkers, but more semantic checkers.
Often the first step in debugging is to attempt reproduce the problem. This can be a non-trivial task
After the bug is reproduced, the input of the program needs to be simplified to make it easier to debug. For example, a bug in a compiler can make it crash when parsing some large source file. However, after simplification of the test case, only few lines from the original source file can be sufficient to reproduce the same crash
After the test case is sufficiently simplified, a programmer can use a debugger to examine program states (values of variables, the call stack) and track down the origin of the problem. Alternatively tracing can be used. In simple case, tracing is just a few print statements, which output the values of variables in certain points of program execution.