Return values in Blockchain / Solidity

Introduction

Return values let a function send back a result after it finishes. This helps you use that result later in your program.

When you want to get the outcome of a calculation from a function.

When you need to pass data from one part of your blockchain code to another.

When you want to check if a transaction was successful and get its details.

When you want to reuse a function's result without repeating the work.

Syntax

Blockchain / Solidity

function functionName(parameters) returns (returnType) {
    // code
    return value;
}

The returns keyword specifies the type of value the function will send back.

Use return inside the function to send the value back.

Examples

This function returns the balance of the current contract as an unsigned integer.

Blockchain / Solidity

function getBalance() public view returns (uint) {
    return address(this).balance;
}

This function adds two numbers and returns the result.

Blockchain / Solidity

function add(uint a, uint b) public pure returns (uint) {
    return a + b;
}

This function returns a fixed string.

Blockchain / Solidity

function getName() public pure returns (string memory) {
    return "Blockchain";
}

Sample Program

This contract has a function multiply that returns the product of two numbers. The testMultiply function calls multiply and returns a string showing the result.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleCalculator {
    function multiply(uint x, uint y) public pure returns (uint) {
        return x * y;
    }

    function testMultiply() public pure returns (string memory) {
        uint result = multiply(3, 4);
        return string(abi.encodePacked("3 times 4 is ", uint2str(result)));
    }

    function uint2str(uint _i) internal pure returns (string memory str) {
        if (_i == 0) {
            return "0";
        }
        uint j = _i;
        uint length;
        while (j != 0) {
            length++;
            j /= 10;
        }
        bytes memory bstr = new bytes(length);
        uint k = length;
        while (_i != 0) {
            k = k-1;
            uint8 temp = (48 + uint8(_i - _i / 10 * 10));
            bstr[k] = bytes1(temp);
            _i /= 10;
        }
        str = string(bstr);
    }
}

Important Notes

Functions can return only one value or multiple values using tuples.

Remember to match the return type in the function signature with the actual returned value.

In blockchain smart contracts, returning values helps verify results without changing the blockchain state.

Summary

Return values let functions send results back to where they were called.

Use returns to specify the type and return to send the value.

Return values help reuse results and check outcomes in blockchain code.