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| -rw-r--r-- | docs/control-structures.rst | 64 |
1 files changed, 62 insertions, 2 deletions
diff --git a/docs/control-structures.rst b/docs/control-structures.rst index f57e7936..974a093f 100644 --- a/docs/control-structures.rst +++ b/docs/control-structures.rst @@ -2,12 +2,62 @@ Expressions and Control Structures ################################## +.. index:: ! parameter, parameter;input, parameter;output + +Input Parameters and Output Parameters +====================================== + +As in Javascript, functions may take parameters as input; +unlike in Javascript and C, they may also return arbitrary number of +parameters as output. + +Input Parameters +---------------- + +The input parameters are declared the same way as variables are. As an +exception, unused parameters can omit the variable name. +For example, suppose we want our contract to +accept one kind of external calls with two integers, we would write +something like:: + + contract Simple { + function taker(uint _a, uint _b) { + // do something with _a and _b. + } + } + +Output Parameters +----------------- + +The output parameters can be declared with the same syntax after the +``returns`` keyword. For example, suppose we wished to return two results: +the sum and the product of the two given integers, then we would +write:: + + contract Simple { + function arithmetics(uint _a, uint _b) returns (uint o_sum, uint o_product) { + o_sum = _a + _b; + o_product = _a * _b; + } + } + +The names of output parameters can be omitted. +The output values can also be specified using ``return`` statements. +The ``return`` statements are also capable of returning multiple +values, see :ref:`multi-return`. +Return parameters are initialized to zero; if they are not explicitly +set, they stay to be zero. + +Input parameters and output parameters can be used as expressions in +the function body. There, they are also usable in the left-hand side +of assignment. + .. index:: if, else, while, do/while, for, break, continue, return, switch, goto Control Structures =================== -Most of the control structures from C or JavaScript are available in Solidity +Most of the control structures from JavaScript are available in Solidity except for ``switch`` and ``goto``. So there is: ``if``, ``else``, ``while``, ``do``, ``for``, ``break``, ``continue``, ``return``, ``? :``, with the usual semantics known from C or JavaScript. @@ -16,7 +66,17 @@ Parentheses can *not* be omitted for conditionals, but curly brances can be omit around single-statement bodies. Note that there is no type conversion from non-boolean to boolean types as -there is in C and JavaScript, so ``if (1) { ... }`` is *not* valid Solidity. +there is in C and JavaScript, so ``if (1) { ... }`` is *not* valid +Solidity. + +.. _multi-return: + +Returning Multiple Values +------------------------- + +When a function has multiple output parameters, ``return (v0, v1, ..., +vn)`` can return multiple values. The number of components must be +the same as the number of output parameters. .. index:: ! function;call, function;internal, function;external |