DFA Implementation C Program

 

✅ Language accepted: Strings ending with 01

Examples of accepted strings: 01, 101, 1101, 00001
Examples of rejected strings: 0, 1, 10, 111, 00

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🔤 DFA States:

• q0: Start state

• q1: Saw 0

• q2: Saw 01 (Accepting state)

✅ C Code:

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

int main() {
    char input[100];
    int state = 0; // Start state is q0

    printf("Enter a binary string: ");
    scanf("%s", input);

    for (int i = 0; i < strlen(input); i++) {
        char ch = input[i];
        switch (state) {
            case 0: // q0
                if (ch == '0') state = 1;
                else if (ch == '1') state = 0;
                else {
                    printf("Invalid input\n");
                    return 1;
                }
                break;
            case 1: // q1
                if (ch == '0') state = 1;
                else if (ch == '1') state = 2;
                else {
                    printf("Invalid input\n");
                    return 1;
                }
                break;
            case 2: // q2
                if (ch == '0') state = 1;
                else if (ch == '1') state = 0;
                else {
                    printf("Invalid input\n");
                    return 1;
                }
                break;
        }
    }

    if (state == 2)
        printf("String is accepted by the DFA.\n");
    else
        printf("String is rejected by the DFA.\n");

    return 0;
}

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🧠 Explanation:

• The DFA moves between states based on the current character.

• Only strings that end in the pattern 01 will leave the DFA in state q2.

• state == 2 is the accepting condition.