#include <stdio.h>
main()
{
    printf("hello, world\n");
}

#include <stdio.h>
main()
{
    int a, b=2;
    char c;
    a = 3;
    c = 'A';
    printf("a = %d\n", a);
    printf("b = %d\n", b);
    printf("c = %c\n", c);
}

#include <stdio.h>
main()
{
    double radius = 10;
    double pi = 3.1415926;
    double circumference;
    double area;

    circumference = radius * 2 * pi;
    area = radius * radius * pi;

    printf("radius = %f\n", radius);
    printf("circumference = %f\n", circumference);
    printf("area = %f\n", area);
    printf("\n\n");

    printf("radius = %f\n", radius = 20);
    printf("circumference = %f\n", radius * 2 * pi);
    printf("area = %f\n", radius * radius * pi);
}

#include <stdio.h>
main()
{
    int i;

    for(i=0; i<20; i++){
        printf("i = %d\n", i);
    }
}