C++ Syntax: for


The for loop corresponds roughly to the FORTRAN do loop. The syntax is:-
for ( init-expr; test-expr; increment-expr) statement
any or all of the expressions insides the brackets may be empty. The sequence is as follows:-
  1. init-expr, if it exists, is executed. Typically this initialises one or more counters, and may also declare them as well.
  2. test-expr is evaluated. If it evaluates to true (nonzero) or is missing then statement, which is often a compound statement is executed. Otherwise the for loop exits.
  3. increment-expr is executed if it exists. Typically this increments one or more counters.
  4. Control returns to step 2 and the test repeated.
For example to sum the contents the 10 element array my_ints:-
Int_t sum = 0;
for (Int_t index=0; index<10; index++) sum += my_ints[index];

Usage Notes

When init-expr is used to declare, as well as initialise a variable, it is defined to have the same scope as the for statement itself, that is to say the innermost compound statement that holds the for loop. Two important consequences:- To break out of a loop use the break statement and to skip directly to the next cycle of a loop use the continue statement.
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