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setting a pointer to NULL, there is no risk of double-freeing memory if the pointer is passed to
free(). Keep in mind that double-freeing memory can lead to very time consuming, confusing, and
difficult to diagnose failures.

Copying too much

char buf[8]; /* tiny buffer, easy to overflow */

printf("What is your name?\n");
scanf("%s", buf); /* WRONG */
scanf("%7s", buf); /* RIGHT */

If the user enters a string longer than 7 characters (- 1 for the null terminator), memory behind the
buffer buf will be overwritten. This results in undefined behavior. Malicious hackers often exploit
this in order to overwrite the return address, and change it to the address of the hacker's malicious
code.

Forgetting to copy the return value of realloc into a temporary

If realloc fails, it returns NULL. If you assign the value of the original buffer to realloc's return value,
and if it returns NULL, then the original buffer (the old pointer) is lost, resulting in a memory leak.
The solution is to copy into a temporary pointer, and if that temporary is not NULL, then copy into
the real buffer.

char *buf, *tmp;

buf = malloc(...);
...

/* WRONG */
if ((buf = realloc(buf, 16)) == NULL)
perror("realloc");

/* RIGHT */
if ((tmp = realloc(buf, 16)) != NULL)
buf = tmp;
else
perror("realloc");

Comparing floating point numbers

Floating point types (float, double and long double) cannot precisely represent some numbers
because they have finite precision and represent the values in a binary format. Just like we have
repeating decimals in base 10 for fractions such as 1/3, there are fractions that cannot be
represented finitely in binary too (such as 1/3, but also, more importantly, 1/10). Do not directly
compare floating point values; use a delta instead.

#include <float.h> // for DBL_EPSILON and FLT_EPSILON
#include <math.h> // for fabs()

int main(void)

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