Question

How to run #include <stdblib.h> like run system("cls")

Answer 1

CLS is a Windows command. OnlineGDB runs on Unix based operating system. Use

system("clear");

instead.

Note: The compiler may reorganize your code for optimization reasons, so don't be surprised if simple programs like

#include <stdio.h>
#include <stdlib.h>

int main()
{
    printf("Type some text then hit ENTER! : ");
//    scanf("%*s");
//    system("clear");
    printf("Hello World");
    return 0;
}

do not work as you would have expected. But if you uncomment those two lines, the screen will be cleared (as the printf calls cannot be optimized together anymore).