extern, for

The extern keyword declares that a variable or a function has external linkage outside of the file it is declared.

for

There are three types of loops in C programming. The for loop is written in C programming using the keyword for. For example:

for (i=0; i< 9;++i){
  printf("%d ",i);
}

Output

0 1 2 3 4 5 6 7 8