whar does assert do in C code example

Example: assert() in c

(Assert Truth of Expression) In the C Programming Language,
assert is a macro that is designed to be used like a function.

Following is syntax for assertion:
			void assert( int expression ); 
            
Case I  : WHEN expression EVALUATES true,
		  nothing happens and the compiler proceeds to execute successive
          statements
Case II : WHEN expression EVALUATES false,
	      the expression, sourcecode filename, and line number are 
          sent to the standard error, and then abort() function is called.