predictiveparsing.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char table[10][10] = {"NT", "a", "b", "A", "aBa", "Error", "B", "@", "bB"};
char buffer[10], stack[10];
int top = -1;
char pop()
{
    return stack[top--];
}
void push(int e)
{
    stack[++top] = e;
}
void display_stack()
{
    int i = top;
    while (i >= 0)
    {
        printf("%c", stack[i]);
        i--;
    }
    printf("\n");
}
char *parse_table(char stack_top, char input_val)
{
    switch (stack_top)
    {
    case 'A':
        switch (input_val)
        {
        case 'a':
            return table[4];
        case 'b':
            return table[5];
        }
        break;

    case 'B':
        switch (input_val)
        {
        case 'a':
            return table[7];
        case 'b':
            return table[8];
        }
    default:
        return table[5];
    }
}

int main()
{
    int ptr = 0, i = 0, j, k, w = 0;
    char *str;
    for (j = 0; j < 3; j++)
    {
        for (k = 0; k < 3; k++)
        {
            printf("%s\t", table[w++]);
        }
        printf("\n");
    }
    printf("Enter string\n");
    scanf("%s", buffer);
    if (buffer[strlen(buffer) - 1] != ';')
    {
        printf("\nString should end with:");
        exit(0);
    }
    push('$');
    push('A');
    while (stack[top] != '$' && (ptr < strlen(buffer)))
    {
        if (stack[top] == buffer[ptr])
        {
            ptr++;
            printf("1.Element popped is %c\n", pop());
        }
        else if (stack[top] == '@')
        {
            printf("2.Element popped is %c\n", pop());
        }
        else
        {
            str = parse_table(stack[top], buffer[ptr]);
            if (strcmp(str, "Error") == 0)
            {
                printf("Error in parsing\n");
                break;
            }
            printf("3.Element popped is %c\n", pop());
            for (i = strlen(str) - 1; i >= 0; i--)
                push(*(str + i));
        }
        display_stack();
    }
    if (stack[top] == '$' && buffer[ptr] == ';')
        printf("String is accepted\n");
    else
    {
        printf("String is no accepted\n");
    }
    return 0;
}