**`assert()`** is a macro (used as a function) in C. `assert()` statements help to verify the assumptions made by the developer. They are useful when debugging a program.

# Library
```c
#include<assert.h>
```

# Declaration
The following is the declaration of `assert()`:
```c
void assert(int exp)
```
`exp:` The expression to be evaluated as non-zero (true) or zero (false). 


If `exp` evaluates to zero, `assert()` sends the error message to 
#key# stderr: standard error stream in C/C++ #key#
and terminates the program by calling `abort()`. On the other hand, normal execution continues if `exp` evaluates to non-zero.


# Disabling `assert()`
We can disable `assert()` statements by defining the `NDEBUG` macro before including `assert.h` in the source file.




#include <stdio.h>
#include <assert.h>
 
int main()
{
    int x = 1;
    assert(x == 1);
    printf("First assert passed");   

    x = 2;
    assert(x == 1);
    // The below line is not printed
    // because assert evaluates to false.
    printf("\nSecond assert passed"); 

    return 0;
}

#include <stdio.h>
#define NDEBUG
#include <assert.h>
 
int main()
{
  // Both prints will be executed
  // as assert statements are disabled
  int x = 1;
  assert(x == 1);
  printf("First assert passed");   

  x = 2;
  assert(x == 1);
  printf("\nSecond assert passed"); 

  return 0;
}

What is assert() in C?

assert() in C verifies assumptions by evaluating expressions; if false, it terminates the program. It can be disabled using NDEBUG.

What is assert() in C?

Library

Declaration

Disabling `assert()`

Code

1. Without `NDEBUG`

2. With `NDEBUG`

What is assert() in C?

Library

Declaration

Disabling assert()

Code

1. Without NDEBUG

2. With NDEBUG

Disabling `assert()`

1. Without `NDEBUG`

2. With `NDEBUG`