# Undefined Behavior & const — C Programming

Source: https://www.geekswithgeeks.com/en/c/c-undefined-behavior

> What C lets you get away with — until it doesn't.

## No safety net

C trusts the programmer completely: it does not check array bounds, initialise variables, or verify pointers. Violating these rules is **undefined behavior** — the program might crash, produce garbage, or appear to "work" until it doesn't.

## Two classics: overflow and garbage

Both compile cleanly and may even "seem" to run — that's what makes undefined behavior dangerous.

```c
int arr[5];
arr[5] = 99;       // buffer overflow: out of bounds

int x;
printf("%d\n", x); // uninitialised: prints garbage
```

## const is a promise

Marking a parameter `const` (e.g. `void print(const char *s)`) tells both the compiler and other readers that the function won't modify it — the compiler then rejects any accidental write.