helloworld.c

hello.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main() {
+  puts("Hello World");
+  printf("The answer is %d\n",42);
+  putchar('\n');
+  fprintf(stdout,"Yes\n");
+
+  write(1,"Yes!",strlen("Yes!"));
+  return 42;
+}

helloworld.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main() {
+  puts("Hello World"); // puts "put string" also prints a newline
+
+  printf("The answer is %d\n",42); // "print formatted"
+
+  putchar('\n'); // Print a single character
+
+  fprintf(stdout,"Yes\n"); // print to a file - in this case standard out
+
+  // All of the above are well known C standard library functions
+  // Under the covers, the actual writing requires a system call.
+  // Linux supports the POSIX API. All of the above ultimately call write: 
+
+  // The system call to send 5 bytes to file descriptor #1 (standout output)
+  write(1, "POSIX", 5 );
+  write(1, " ROCKS", strlen(" ROCKS"));
+  return 42;
+}