9 Statements [stmt.stmt]

The for statement

for ( init-statement condition${}_{opt}$ ; expression${}_{opt}$ ) statement

is equivalent to

{
	init-statement
	while ( condition ) {
		statement
		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. [ Note: 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. [ Example:

int i = 42;
int a[10];

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

int j = i;          // j = 42

 — end example ]