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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <ctype.h>
  4.  
  5. char stack[100][10];
  6. int top = -1;
  7. int pos = 0;
  8. char input[100];
  9.  
  10. // Push
  11. void push(const char *s)
  12. {
  13.     strcpy(stack[++top], s);
  14. }
  15.  
  16. // Pop
  17. void pop()
  18. {
  19.     top--;
  20. }
  21.  
  22. // Print Stack
  23. void printStack()
  24. {
  25.     for (int i = 0; i <= top; i++)
  26.         printf("%s", stack[i]);
  27.     printf("\n");
  28. }
  29.  
  30. // Reduce with lookahead
  31. int reduce(char lookahead)
  32. {
  33.     // F -> id
  34.     if (top >= 0 &&
  35.         stack[top][0] >= 'a' &&
  36.         stack[top][0] <= 'z')
  37.     {
  38.         pop();
  39.         push("F");
  40.         return 1;
  41.     }
  42.  
  43.     // F -> (E)
  44.     if (top >= 2 &&
  45.         strcmp(stack[top-2], "(") == 0 &&
  46.         strcmp(stack[top-1], "E") == 0 &&
  47.         strcmp(stack[top], ")") == 0)
  48.     {
  49.         pop(); pop(); pop();
  50.         push("F");
  51.         return 1;
  52.     }
  53.  
  54.     // T -> T * F
  55.     if (top >= 2 &&
  56.         strcmp(stack[top-2], "T") == 0 &&
  57.         strcmp(stack[top-1], "*") == 0 &&
  58.         strcmp(stack[top], "F") == 0)
  59.     {
  60.         pop(); pop(); pop();
  61.         push("T");
  62.         return 1;
  63.     }
  64.  
  65.     // T -> F
  66.     if (top >= 0 &&
  67.         strcmp(stack[top], "F") == 0)
  68.     {
  69.         pop();
  70.         push("T");
  71.         return 1;
  72.     }
  73.  
  74.     // ❗ مهم: E -> E + T (مع check للـ lookahead)
  75.     if (top >= 2 &&
  76.         strcmp(stack[top-2], "E") == 0 &&
  77.         strcmp(stack[top-1], "+") == 0 &&
  78.         strcmp(stack[top], "T") == 0)
  79.     {
  80.         // لو فيه ضرب جاي → متعملش reduce
  81.         if (lookahead == '*')
  82.             return 0;
  83.  
  84.         pop(); pop(); pop();
  85.         push("E");
  86.         return 1;
  87.     }
  88.  
  89.     // E -> T
  90.     if (top >= 0 &&
  91.         strcmp(stack[top], "T") == 0)
  92.     {
  93.         pop();
  94.         push("E");
  95.         return 1;
  96.     }
  97.  
  98.     return 0;
  99. }
  100.  
  101. int main()
  102. {
  103.     printf("Enter an Expression:\n");
  104.     fgets(input, 100, stdin);
  105.  
  106.     while (input[pos])
  107.     {
  108.         // Ignore spaces
  109.         if (isspace(input[pos]))
  110.         {
  111.             pos++;
  112.             continue;
  113.         }
  114.  
  115.         char temp[2] = {input[pos], '\0'};
  116.         push(temp);
  117.         pos++;
  118.  
  119.         printf("Shift: ");
  120.         printStack();
  121.  
  122.         // 👇 هنا بقى بنبعت lookahead
  123.         while (reduce(input[pos]))
  124.         {
  125.             printf("Reduce: ");
  126.             printStack();
  127.         }
  128.     }
  129.  
  130.     // Final reductions
  131.     while (reduce('\0'))
  132.     {
  133.         printf("Reduce: ");
  134.         printStack();
  135.     }
  136.  
  137.     if (top == 0 && strcmp(stack[0], "E") == 0)
  138.         printf("String Accepted\n");
  139.     else
  140.         printf("String Rejected\n");
  141.  
  142.     return 0;
  143. }
Success #stdin #stdout 0s 5320KB
comments (?)
stdin
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a  +  b
stdout
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Enter an Expression:
Shift: a
Reduce: F
Reduce: T
Reduce: E
Shift: E+
Shift: E+b
Reduce: E+F
Reduce: E+T
Reduce: E
String Accepted
https://ideone.com/3LqHoL
language:
C (gcc 8.3)
created:
22 hours ago
visibility:
public

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