Lesson 3: Fund Me

[vicshi06]

Hi.

When I was going through Lesson 3, I saw that the addressToAmountFunded is followed by a +=. However, what is the difference between addressToAmountFunded[msg.sender] += msg.value and addressToAmountFunded[msg.sender] = msg.value? Can someone please explain? Thanks!

[cromewar]

Hello @vicshi06 Yeah this is a difference, let's see.

The = is for assignation, you are saying that whatever is on the right side should be stored on the left side, example:

variable a = 50 this meas variable a <- 50

Quite easy right?

And += means add to the current value, let's suppose we have another variable called b which has the value of 5, so if we say:

b += 1 this means we are saying, add 1 to whatever is on variable b: 5 + 1.

I hope this info might help.

[vicshi06]

Okay I understand the examples you gave, but what does the += mean in the context of addressToAmountFunded[msg.sender] += msg.value. Does that mean every time someone sends me money, that person is being added to the array?

If we replace += with =, does that mean that person is not being added to the array?

[cromewar]

Setting += you are adding both, you are saying that what ever is already there should be added using the new value, if you use = you are just saying you are going to replace whatever is in there with the new value.

[vicshi06]

Thanks so much!

[vicshi06]

One more question actually, does mapping function in solidity automatically create an array?

[cromewar]

Hello @vicshi06, sorry for the delay, mappings are it's own type and should not be considered as arrays, check this out for more info: https://medium.com/upstate-interactive/mappings-in-solidity-explained-in-under-two-minutes-ecba88aff96e