C: getchar

hi,

once again i hit a very simple problem i am unable to resolve. I using Visual Studio 2010, but am compiling for C.


THis:

Code:

---

        char i=45;
        while(i=getchar() != EOF)
        {

---

should imo work perfectly (yes, no real code, just to demonstrate the issue), but it doesnt. Getchar() always returns 0x01. Why is that?
This, in contrast, works perfectly fine:

Code:

---

        char i=45;

        while(i!= EOF)
        {
i=getchar();

---

Shouldnt an assignment always return the assigned value?

When you do:

Code:

---

while( i = getchar() != EOF )

---

You are really doing:

Code:

---

while( i = ( getchar() != EOF ) )

---

So, it gets the character, compares it against the EOF character. It's most likely not equal to it, and so that boolean will become 1 and get assigned to i. This happens because the != operator has a higher precedence than the assignment operator.

There is another problem with your code.
EOF is usually defined as the int -1. If you assign it to a char then the value will be truncated and the test will never be true.
BTW that is the reason why getchar() returns an int and not a char.
Kurt