why do we use return 0 in C language ?

The return indicates how a program terminated, either successfully or otherwise. Since the error state likely needs more of an explanation than if a program finishing successfully, 0 was chosen to indicate success (i.e. you only need more details if you've failed to execute).

Most programs have an assortment of failed return values that correspond to some error codes (for example, 1-failed to open file, 2-failed to write to file, 3-file not found, so on). This allows the operator and/or script that's executing your application to know why it failed, not simply that it has failed.

most programmes return error code; so that the user can fix or track the error if it occures.

so '0' means no error.

Simply we can thought as

your program always run under operating system like windows. simply

int main()

function is a integer return type. if the return is 0 it's send a message to os is that the program is OK no error is generated while running the program and exit is success.

if you use

void main()

you don't have to return anything because it is void return type.OS automatically manage it.but you unable to track that the program run correctly or not.(i am not sure about it , i told it from my experience and learning )