What does !x mean, i understand !(x>30) means x can't be greater than 30 but this '!x' is just confusing me

Question

the not operator(!)

Answer 1

It's used for negating booleans and integers.
For booleans: TRUE becomes FALSE and FALSE becomes TRUE.
For integers: 0 becomes 1 and any non-zero value becomes 0.)

For example;

int x = 100;
if(x) { return; } // evaluates TRUE
if(!x) { return; } // evaluates FALSE, will not return (100 becomes 0)

int x = 0;
if(x) { return; } // evaluates FALSE, will not return
if(!x) { return; } // evaluates TRUE (0 becomes 1)

bool b = true;
if(b) { return; } // true
if(!b) { return; } // false

bool b = false;
if(b) { return; } // false
if(!b) { return; } // true

It also works when assigning new values.

int x = 100;
int y = !x; // 0
int z = !y; // 1
int q = !!x; // 1
int k = !(60<30); // 1

Pay attention to what happened to Q. The NOT is applied twice, so the first NOT (0) becomes NOT'ed again to 1. You may see this in some cases but it's nothing special.

Answer 2

Basically the if statement checks if the value of a given condition is zero or non zero.
Code:

if(x)
cout<<"and";

"abc" will only be printed if the value of x is anything except 0, i.e. abc will be printed for x = 6 as well as x = -5, but not for x =0

In a similar way, if the code is:

if(!x)
cout<<"xyz<<;

"xyz" will only be printed for x = 0, and won't be printed for x =7 or x= -10

What !x (not x) does is that it changes the non zero value to a zero value and vice versa