check_for _a_valid_sentence.c

// C program to validate a given sentence for a set of rules
#include<stdio.h>
#include<string.h>
#include<stdbool.h>

// Method to check a given sentence for given rules
bool checkSentence(char str[])
{
    // Calculate the length of the string.
    int len = strlen(str);

    // Check that the first character lies in [A-Z].
    // Otherwise return false.
    if (str[0] < 'A' || str[0] > 'Z')
        return false;

    //If the last character is not a full stop(.) no
    //need to check further.
    if (str[len - 1] != '.')
        return false;

    // Maintain 2 states. Previous and current state based
    // on which vertex state you are. Initialise both with
    // 0 = start state.
    int prev_state = 0, curr_state = 0;

    //Keep the index to the next character in the string.
    int index = 1;

    //Loop to go over the string.
    while (str[index])
    {
        // Set states according to the input characters in the
        // string and the rule defined in the description.
        // If current character is [A-Z]. Set current state as 0.
        if (str[index] >= 'A' && str[index] <= 'Z')
            curr_state = 0;

        // If current character is a space. Set current state as 1.
        else if (str[index] == ' ')
            curr_state = 1;

        // If current character is [a-z]. Set current state as 2.
        else if (str[index] >= 'a' && str[index] <= 'z')
            curr_state = 2;

        // If current state is a dot(.). Set current state as 3.
        else if (str[index] == '.')
            curr_state = 3;

        // Validates all current state with previous state for the
        // rules in the description of the problem.
        if (prev_state == curr_state && curr_state != 2)
            return false;

        if (prev_state == 2 && curr_state == 0)
            return false;

        // If we have reached last state and previous state is not 1,
        // then check next character. If next character is '\0', then
        // return true, else false
        if (curr_state == 3 && prev_state != 1)
            return (str[index + 1] == '\0');

        index++;

        // Set previous state as current state before going over
        // to the next character.
        prev_state = curr_state;
    }
    return false;
}

// Driver program
int main()
{
    char *str[] = { "I love cinema.", "The vertex is S.",
                    "I am single.", "My name is KG.",
                    "I lovE cinema.", "GeeksQuiz. is a quiz site.",
                    "I love Geeksquiz and Geeksforgeeks.",
                    "  You are my friend.", "I love cinema" }
    int str_size = sizeof(str) / sizeof(str[0]);
    int i = 0;
    for (i = 0; i < str_size; i++)
     checkSentence(str[i])? printf("\"%s\" is correct \n", str[i]):
                            printf("\"%s\" is incorrect \n", str[i]);

    return 0;
}