Difference between while(i=0) and while(i==0)

Question

In my exam the following problem appeared in C++

Code:

int i, n;
int* A
cin >> n;
A = new int[n]
for(int i = 0; i < n; i++) cin >> A[i];

while(i = 0){
   cout << A[i] << endl;
   i--;
}
}

What will be the output? I think that it should go into indefinite loop!

Answer 1

while (i = 0) will assign the value 0 to i and then check whether the value of the expression (which is the value assigned, i.e. 0) is non-zero. In other words, it won't execute the body of the loop even once... it'll just set i to 0. It'll also raise a warning on any decent compiler, as it's a common typo.

Following the same logic, while (i = 1) would assign the value 1 to i and always execute the loop body... only a break (or exception) within the loop would terminate it.

(Many other languages don't have this issue as widely, as they require an expression of a boolean type for conditions such as while and if. Such languages still often have a problem with while (b = false) though.)