Kernighan & Ritchie code example confusion

Question

Is there any reason of the second 'c = getchar()' mention in this code example?

#include <stdio.h>
/* copy input to output; 1st version */  

int main(void) {

    int c;

    c = getchar();
    while (c != EOF) {
        putchar(c);
        c = getchar(); // <-- I mean this one.
    }
    return 0;
}

Answer 1

c = getchar();                    //read for the first time before entering while loop
    while (c != EOF) {
        putchar(c);
        c = getchar();            // read the next input and go back to condition checking
    }
    return 0;

1. first getchar() reads the first time input character.
2. second getchar() keeps on reading next input(s), untill a EOF

In other words, the purpose of while (c != EOF) is to keep on checking whether the c is EOF or not. if c is not changed, then the while() loop is meaningless, isn't it? The second getch() is responsible for chnaging the value of c in each iteration.

Answer 2

yes, so it wont putchar EOF.

It reads the first character, checks that its not EOF, then putChars it, then gets another char, back to the top of the while loop and checks its not EOF.

Answer 3

The second c = getchar() is to read another char and yet anther one until EOF is met.

Answer 4

first c = getchar(); will only work Once, but c = getchar(); inside while loop will work every time until c != EOF.

c = getchar(); // Read value of `c` if `c != EOF` it will enter while loop else it will exit
while (c != EOF) {  // checking condition
   putchar(c);     //printing value of c
   c = getchar(); // again getting new value of c and checking in while loop,  
                    //if condition is true it will continue, else it will exit
}

Answer 5

It's there because a while loop tests at the top but you really need the test in the middle. An alternative to duplicating code above the loop and inside it, is using break.

while (1) {
    c = getchar();
    if (c == EOF) break; /* test in middle */
    putchar(c);
}

Answer 6

That's my inattention. I was running in terminal this version of code:

while((c = getchar()), c != EOF) {
putchar(c);
}

and couldn't see the difference between results. Stupid situation. Thanks to all anyway.