void assert (int expression);
Evaluate assertion

If the argument expression of this macro with functional form compares equal to zero (i.e., the expression is false), a message is written to the standard error device and abort is called, terminating the program execution.

The specifics of the message shown depend on the specific implementation in the compiler, but it shall include: theexpression whose assertion failed, the name of the source file, and the line number where it happened. A usual expression format is:

Assertion failed: expression, file filename, line line number

This macro is disabled if at the moment of including assert.h a macro with the name NDEBUG has already been defined. This allows for a coder to include many assert calls in a source code while debugging the program and then disable all of them for the production version by simply including a line like:
#define NDEBUG at the beginning of its code, before the inclusion of assert.h.

Therefore, this macro is designed to capture programming errors, not user or running errors, since it is generally disabled after a program exits its debugging phase.

/* assert example */
#include <stdio.h>
#include <assert.h>

void print_number(int* myInt) {
  assert (myInt!=NULL);
  printf ("%dn",*myInt);

int main ()
  int a=10;
  int * b = NULL;
  int * c = NULL;


  print_number (b);
  print_number (c);

  return 0;