写一个 C function 以英文句子为参数，返回句子中最长的单词

Question

I have an assignment that requires me to write a function to take in an array containing an English sentence and return the length of the longest word in that sentence. This is the code I have so far:

int longWordLength(char *s); // Function prototype

int main() {
    char str[80], *p;

    printf("Enter a string: \n");
    fgets(str, 80, stdin);

    if (p = strchr(str,'\n'))
        *p = '\0'; //converts newline to null

    printf("longWordLength(): %d\n", longWordLength(str));
    return 0;
}

int longWordLength(char *s) {
    int count = 0, max = 0;
    while (*s++ != '\0') {
        if ((*s >= 'a' && *s <= 'z') || (*s >= 'A'&& *s <= 'Z')) {
            count++;
        } else {
            if (count > max) {
                max = count;
                count = 0;
            } else
                count = 0; // word is not the longest
        }
    }
    return max;
}

I have tried for a long time to diagnose the issue but to no avail.

This works with certain test case like:

Test Case 1:

Enter a string:  
I am happy.
longWordLength(): 5

but for a test case like Test Case 4:

Enter a string:  
Hello
longWordLength(): 4 <- it prints 4 instead of 5.

I am not allowed to use any library other than the <string.h> as it is for my school assignment. Seeking anyone's kind guidance on my issue as I really can't seem to figure out the issue. Thank you in advanced.

Answer 1

The problem is in while (*s++ != '\0') { : you increment the string pointer before testing the character it points to. Just change to code to:

    for (; *s != '\0'; s++) {
        ...

Note however that the last word will not be tested the maximum length if it is not followed by some separator such as a space or a newline, which you would have stripped.

Note that stripping the trailing newline is not required for longWordLength() to determine the correct count.

Here is a modified version:

#include <stdio.h>

int longWordLength(const char *s); // Function prototype

int main() {
    char str[80];

    printf("Enter a string: \n");
    if (!fgets(str, sizeof str, stdin))
        return 1;

    // no need to strip the newline for this test:
    printf("longWordLength(): %d\n", longWordLength(str));
    return 0;
}

int longWordLength(const char *s) {
    int count = 0, max = 0;
    for (;; s++) {
        if ((*s >= 'a' && *s <= 'z') || (*s >= 'A'&& *s <= 'Z')) {
            count++;
        } else {
            if (count > max) {
                max = count;
            }
            if (*s == '\0')
                break;
            count = 0;  // reset the counter for the next word
        }
    }
    return max;
}