// 1. This line is a comment that is ignored by compiler.

// 2. include standard library for input/output. Allows to print to shell
#include <stdio.h> 

// 3. execution start inside this **function** named main. 
int main() 
{ // start of main function

    // 4. prints to the shell
    printf("Hello, world\n");
    return 0; /* 5. returns integer 0 */

} // end of main function

// Makefile
run: 
    gcc main.c -o main
    ./main

#include <stdio.h> 
int main() 
{ 
    printf("printing the integer constant %d\n", 1);
    printf("printing the integer constant %d\n", 100);
    
    printf("printing the float constant %f\n", 1.5);
    printf("printing the float constant %f\n", 15.6);

    return 0;
} 

printf("circumference is %f", 2*3.14*5);