C - General Programming - Return value of a if statement without any condition

To test a condition in a if statement without any condition, the result has to be other than 0 to test a true condition.

Let's see an example of a if statement without any condition:

#include	<stdio.h>

int     checkIt()
{
  int	a;

  a = 0;
  if (a == 0)
    return (-1);
  return (0);
}

int     main()
{
  int   number;

  number = checkIt();
  if (number)
    printf("True - Value was %d.\n", number);
  else
    printf("False - Value was %d.\n", number);
  return (0);
}

Compile and execute it:

$ gcc main.c && ./a.out

Result:

$ True - Value was -1.

In this example above we can see that if the return value of the number variable is 0.
If this value is equal to 0, the if statement is considered as false.

Note that this value can be a negative or a positive one.
Example: -1, -900, 892, 12909093 are the same.

Let's try another example of a if statement with the contrary of a value, with the ! operator.

#include	<stdio.h>

int     checkIt()
{
  int	a;

  a = 0;
  if (a == 0)
    return (-5451);
  return (0);
}

int     main()
{
  int   number;

  number = checkIt();
  if (!number)
    printf("True - Value was %d.\n", number);
  else
    printf("False - Value was %d.\n", number);
  return (0);
}

Result:

$ False -  Value was -5451.