Count blanks, tabs, and newlines

K&R Exercise 1-8: write a program that reads input and counts how many blanks, tabs, and newlines it saw.

A blank here is a space character. Tabs and newlines are counted on their own. Letters, digits, and punctuation are ignored.

You already have getchar() and EOF. Same read loop; three counters this time.

Three characters to watch

A blank is ' ' (the space bar). A tab is '\t' (the Tab key). A newline is '\n' (Return). The loop is the one from the earlier exercises: while ((c = getchar()) != EOF). Each time around, look at c and increment the matching counter.

Write the program

Create a file called count-blanks.c:

#include <stdio.h>

int main(void)
{
    int c;
    int blanks, tabs, newlines;

    blanks = tabs = newlines = 0;

    while ((c = getchar()) != EOF) {
        if (c == ' ') {
            ++blanks;
        } else if (c == '\t') {
            ++tabs;
        } else if (c == '\n') {
            ++newlines;
        }
    }

    printf("%d blanks, %d tabs, %d newlines\n", blanks, tabs, newlines);
    return 0;
}

Three integers, all start at zero. else if is fine: one character cannot be a space and a tab at once.

Compile and run

In Terminal, from the folder that holds count-blanks.c:

gcc count-blanks.c -o count-blanks
./count-blanks

Type this exactly — on the second line, press Tab between the words, not space:

The quick brown fox jumps over the lazy dog.
one	two	three

Press Return after the second line, then Ctrl+D on an empty line. You should see:

8 blanks, 2 tabs, 2 newlines

The pangram has eight spaces. one, two, and three are separated by two tabs. Each Return is a newline.

If the second line was typed with spaces, those count as blanks and the tab total stays at zero.

If gcc is missing, finish Getting your macOS ready for C first.

How to send EOF

On macOS, Ctrl+D after a newline is end-of-file — same as getchar() and EOF. The program then prints the three totals and exits.

Check the numbers

Count the spaces in the pangram by hand: there are eight. If the program prints 8, 2, and 2, the three tests are wired to the right characters.

What you should take away

getchar gives you one character at a time. Comparing it to ' ', '\t', and '\n' is how you classify input. Three counters stay independent — a tab is not a blank.

Next

→ Collapse runs of blanks — Exercise 1-9