You are mixing C with C ++. The first thing to do is decide whether to program in one language or another. As it seems to be C ++, I'll try to hit it:
#include <iostream>
using namespace std;
int main() {
float lado, area;
cout << "digite o lado";
cin >> lado;
area = lado * lado;
cout << area;
return 0;
}
See running on ideone .
The changes I've made:
- I put the right header,
iostream
that contains cin
and cout
. What you are using is C header.
- I put
using
so I do not have to call the method by full name, so you do not have to use std::cin
, for example.
- And I have hit the type of the function
main()
that returns a int
, so you have to type it.
Then, if you want, you can improve to make the output more presentable.
I gave one an organized code as well. Get used to doing this. It's important.
Fixing these things should compile. My compiled. I do not know in DEV C ++ because it is a pretty bad IDE.