The for loop

   1 + 2 + 3 + ... + N

using a loop. Partial sums are accumulated in the variable N

   for(i = 1; i <= N; i++ )
      s := s + i;
	  
   // more idiomatic version:
   for(i = 1; i <= N; i++ )
      s += i;

The first clause in for( *; *; *) initializes the loop counter. The second tests to see if the current loop counter is valid. The third increments it by one unit. This is the syntax in general: initialize counter; test it; increment it.

The body of a for loop can be a block, i.e., a sequence of statements enclosed by curly braces:

   for(i = 1; i <= N; i++ ) {
      s := i;
	  printf("sum(%d) = %d\n", i, s);
   }