Lesson 4: what does the line "addressToAmountFunded[msg.sender] += msg.value;" in Fundme.sol means?

[saurav3232]

In the Contract FundMe in lesson 4 at line 20 at time 4:29:46 the code is "addressToAmountFunded[msg.sender] = msg.value;"
, but later the code has been changed to "addressToAmountFunded[msg.sender] += msg.value;" , what does the new code signifies?

[JamesMckenna]

addressToAmountFunded[msg.sender] = msg.value;

An address on the blockchain has sent funds to your contract. Keep track of that blockchain address and the amount that was sent to your contract from that address.

addressToAmountFunded[msg.sender] += msg.value;

An address on the blockchain has sent funds to your contract. Keep track of that blockchain address and the amount that was sent to your contract from that address. If that address has previously sent funds to your contract, add the new value to the last value that was sent.

addressToAmountFunded[msg.sender] += msg.value;

is short hand for

addressToAmountFunded[msg.sender] = addressToAmountFunded[msg.sender] + msg.value;

SEE: https://docs.soliditylang.org/en/v0.8.13/control-structures.html?#scoping-and-declarations
Solidity initializes all uint variables to 0. So in the case of uint variables types.

addressToAmountFunded[msg.sender] += msg.value;

or

addressToAmountFunded[msg.sender] = addressToAmountFunded[msg.sender] + msg.value;

is a better way to write it than

addressToAmountFunded[msg.sender] = msg.value;

[saurav3232]

Thank you , got it

[JamesMckenna]

yw