Program to find the longest word in a string

Question

I wrote a program to find the longest word in a string and print the number of letters in the longest word. But the code is not printing. I analyzed the program many times but I could not find the solution.

#include <stdio.h>
#include <string.h>

int main() {
    char string[100] = "Hello Kurnool";
    int i = 0, letters = 0, longest = 0;

start:

    for (; string[i] !=' '; i++) {
        letters++;  
    }

    if (letters >= longest)
        longest = letters;

    if (string[i] == ' ') {
        letters = 0;
        i++;
        goto start;
    }

    printf("%d", longest);

    return 0;
} 

Answer 1

Using goto is highly discouraged. You should convert your code to use a loop.

The main problem in your code is you do not stop the scan when you reach the end of the string.

Here is a modified version:

#include <stdio.h>

int main() {
    char string[100] = "Hello Kurnool";
    int i, letters, longest = 0, longest_pos = 0;

    for (i = 0; string[i] != '\0'; i++) {
        for (letters = 0; string[i] != '\0' && string[i] != ' '; i++) {
            letters++;  
        }
        if (letters > longest) {
            longest = letters;
            longest_pos = i - longest;
        }
    }    
    printf("longest word: %d letters, '%.*s'\n",
           longest, longest, string + longest_pos);

    return 0;
}

Note that the implementation can be simplified into a single loop:

#include <stdio.h>

int main() {
    char string[100] = "Hello Kurnool";
    int i, start = 0, longest = 0, longest_pos = 0;

    for (i = 0; string[i] != '\0'; i++) {
        if (string[i] == ' ') {
            start = i + 1;
        } else {
            if (i - start > longest) {
                longest = i - start;
                longest_pos = start;
            }
        }
    }    
    printf("longest word: %d letters, '%.*s'\n",
           longest, longest, string + longest_pos);

    return 0;
}

Answer 2

Below is my approach. You should use C's string manipulation functions. This is the correct way to deal with strings in C.

In the code below, first I acquire the required bytes to store the input string in heap. Then I use strtok to split the string into tokens based on a delemeter and get the length of each sub string. Finally I free the space that I have allocated with malloc.

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

#define phrase "Hello Kurnool"
int main()
{
    char* string = malloc(strlen(phrase)+1);
    strcpy(string,phrase);
    int longest=0;
    char *token;
    char delimeter[2] = " ";

   /* get the first token */
   token = strtok(string, delimeter);

   /* walk through other tokens */
    while( token != NULL ) {
        printf( " %s\n", token );
        if(longest < strlen(token)){
            longest = strlen(token);
        }
        token = strtok(NULL, delimeter);
   }
    printf("%d",longest);
    free(string);
    return 0;
}

Answer 3

People say - dont use goto but there is nothing inherently wrong with goto. Only thing is if goto is not used judiciously, it makes code more difficult to understand and maintain. For example, the way you have used it in your program ( instead of goto, a loop is perfect fit in such cases). Check this:
To use goto or not?
What is wrong with using goto?

Coming to your code, the for loop condition does not have check for terminating null character

for (; string[i] !=' '; i++) {

Hence it will not stop at the end of string.
To find the number of letters in longest word of string, you can do:

#include <stdio.h>
#include <string.h>

int main() {
    char string[100] = "Hello Kurnool";
    int i, letters = 0, longest = 0;

    for (i = 0; string[i] != '\0'; i++) {
        if (string[i] != ' ') {
            letters++;
            if (letters > longest) {
                longest = letters;
            }
        } else {
            letters = 0;
        }
    }

    printf("longest : %d\n", longest);

    return 0;
}

Answer 4

First of all,Please avoid using Goto, it is not a good practice.

Secondly, your loop will run infinite times when it iterates the second time because:

for(;string[i]!=' ';i++) // Here String[i] will never be equal to ' ' As there is no white space after your last word.

Answer 5

You can never expect what might be going wrong with your program if you are using

goto statement

which is never advisable to use rather it's bad programming if you use it. Secondly it looks like you are stuck in an infinite loop so her is a solution to your problem:

#include<stdio.h>
#include<string.h>
void main()
{
    char s[1000];
    scanf("%s",s);
    int i=0;
    int letters;
    int longest=0;
    while(s[i]!=NULL)
   {
      if(s[i]==' ')
      {
         if(longest>=letters)
              {longest=letters;}
         letters=0;
       }
      else
         {letters++;}
    }
printf("%d\n",longest);
}

So, what I have done is assuming a string s which is the input given by the user. You itterate through s till the last input given by the user after which it encounters a NULL character. Now you are searching for the length of the longest word, so you create a variable letters for counting the no. of letters in each word of the string. And if the string s encounters a space indicating the end of a word, then you check if the variable longest is greater than or less than the word count. And again you initialize letters to 0, so that it can start counting the next word from 0 again.So, by this method at the end i.e. after the while loop terminates we get our required output which is stored in the variable longest. So, I guess this will print the no. of letters in the longest word.