in C++

<bits/stdc++.h> is a non-standard header file provided by the GCC that allows developers to include multiple standard C++ libraries using a single line of code. It is widely used in competitive programming to speed up development.

However, since it is not part of the C++ standard, it is not portable and should be avoided in production-level software.

• Works only with GCC-based compilers (not supported in MSVC)
• Increases compilation time due to inclusion of unnecessary headers

Example: To use the sqrt() function, you do not need to include the <cmath> header separately if <bits/stdc++.h> is already included.

#include <bits/stdc++.h>
using namespace std;

int main() {

    cout << sqrt(25); 
    return 0;
}

5

But if we use <iostream> header file, we have to write <cmath> header file to run the sqrt( ) function otherwise compiler shows that 'sqrt' was not declared in this scope.

#include <iostream>
#include <cmath>
using namespace std;

int main() {

    cout << sqrt(25);
    return 0;
}

5

So, the user can either use it and save the time of writing every include or save the compilation time by not using it and writing necessary header files.