cd7 shift reduce

//S->AB A->a B->b
//ab accepted
//aa not accepted

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

typedef struct {
    char left;       // Non-terminal
    char right[10];  // Production rule right side
} Rule;

int main() {
    int rule_count, i = 0;
    char input[20], stack[50] = "", temp[50];
    Rule rules[10];

    // Input production rules
    printf("Enter the number of production rules: ");
    scanf("%d", &rule_count);
    getchar(); // Consume newline

    printf("Enter the production rules (e.g., S-->AB|a):\n");
    for (i = 0; i < rule_count; i++) {
        fgets(temp, sizeof(temp), stdin);
        temp[strcspn(temp, "\n")] = '\0';
        rules[i].left = temp[0];               // Left-hand side
        strcpy(rules[i].right, temp + 3);      // Right-hand side
    }

    // Input string to parse
    printf("Enter the input string: ");
    scanf("%s", input);

    printf("%-14s %-14s %-14s\n", "Stack", "Input", "Action");
    printf("-------------- -------------- --------------\n");

    i = 0;
    while (1) {
        // Shift operation
        if (i < strlen(input)) {
            strncat(stack, &input[i++], 1);
            printf("%-15s%-15sShift %c\n", stack, &input[i], input[i - 1]);
        }

        // Reduction attempt
        int reduced = 0;
        for (int j = 0; j < rule_count; j++) {
            int len = strlen(rules[j].right);
            if (strlen(stack) >= len &&
                strcmp(stack + strlen(stack) - len, rules[j].right) == 0) {
                stack[strlen(stack) - len] = '\0'; // Remove matched part
                strncat(stack, &rules[j].left, 1);
                printf("%-15s%-15sReduce %c-->%s\n", stack, &input[i], rules[j].left, rules[j].right);
                reduced = 1;
                break;
            }
        }

        // Check for acceptance
        if (!reduced && i == strlen(input) && stack[0] == rules[0].left && stack[1] == '\0') {
            printf("\nAccepted\n");
            return 0;
        }

        // Reject if no reduction possible and input is consumed
        if (!reduced && i == strlen(input)) {
            printf("\nNot Accepted\n");
            return 0;
        }
    }
}