9 Statements [stmt.stmt]

9.5 Iteration statements [stmt.iter]

9.5.3 The for statement [stmt.for]

The for statement
for ( init-statement condition ; expression ) statement
is equivalent to
	while ( condition ) {
		expression ;
except that names declared in the init-statement are in the same declarative region as those declared in the condition, and except that a continue in statement (not enclosed in another iteration statement) will execute expression before re-evaluating condition.
Thus the first statement specifies initialization for the loop; the condition ([stmt.select]) specifies a test, sequenced before each iteration, such that the loop is exited when the condition becomes false; the expression often specifies incrementing that is sequenced after each iteration.
end note
Either or both of the condition and the expression can be omitted.
A missing condition makes the implied while clause equivalent to while(true).
If the init-statement is a declaration, the scope of the name(s) declared extends to the end of the for statement.
int i = 42;
int a[10];

for (int i = 0; i < 10; i++)
  a[i] = i;

int j = i;          // j = 42
end example