Count words in a given string

Given a string, count number of words in it. The words are separated by following characters: space (‘ ‘) or new line (‘\n’) or tab (‘\t’) or a combination of these.

There can be many solutions to this problem. Following is a simple and interesting solution.
The idea is to maintain two states: IN and OUT. The state OUT indicates that a separator is seen. State IN indicates that a word character is seen. We increment word count when previous state is OUT and next character is a word character.

/* Program to count no of words from given input string. */ #include <stdio.h>   #define OUT 0 #define IN  1   // returns number of words in str unsigned countWords(char *str) {     int state = OUT;     unsigned wc = 0;  // word count       // Scan all characters one by one     while (*str)     {         // If next character is a separator, set the state as OUT         if (*str == ' ' || *str == '\n' || *str == '\t')             state = OUT;           // If next character is not a word separator and state is OUT,         // then set the state as IN and increment word count         else if (state == OUT)         {             state = IN;             ++wc;         }           // Move to next character         ++str;     }       return wc; }   // Driver program to tes above functions int main(void) {     char str[] = "One two          three\n  four\nfive  ";     printf("No of words: %u\n", countWords(str));     return 0; }

Output:

No of words: 5

Time complexity: O(n)

This article is compiled by Narendra Kangralkar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.