[Solved] Understanding an exercise in K&R [closed]

Question

The while loop continues to execute as long as it gets a character from stdin that is not EOF:

while((c = getchar()) != EOF)

Two char variables are declared: c and lastc. For this logic to work, the current character and the previous character must be known. Initially, lastc does not have a value, but it’s used nonetheless:

if(lastc != ' ')
    putchar(c);

It is possible that when the program starts lastc will have a garbage value that != ' '. It would be a very good idea to define this variable when you declare it to a sane value:

int c, lastc=" ";

The logic is as follows:

The current character is read from stdin. If it is not the space character (' '), it is written to stdout. If it is a space, the space is written to stdout only if the previous character was not a space. If the previous character was a space, the current space is ignored as to make only one space printed if there is a series of space characters in stdin.

Accepted Answer

The while loop continues to execute as long as it gets a character from stdin that is not EOF:

while((c = getchar()) != EOF)

Two char variables are declared: c and lastc. For this logic to work, the current character and the previous character must be known. Initially, lastc does not have a value, but it’s used nonetheless:

if(lastc != ' ')
    putchar(c);

It is possible that when the program starts lastc will have a garbage value that != ' '. It would be a very good idea to define this variable when you declare it to a sane value:

int c, lastc=" ";

The logic is as follows:

The current character is read from stdin. If it is not the space character (' '), it is written to stdout. If it is a space, the space is written to stdout only if the previous character was not a space. If the previous character was a space, the current space is ignored as to make only one space printed if there is a series of space characters in stdin.