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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 cursor = 0;
  8. char buffer[100];
  9.  
  10. void push(const char *symbol) {
  11.     strcpy(stack[++top], symbol);
  12. }
  13.  
  14. void pop() {
  15.     if (top >= 0) top--;
  16. }
  17.  
  18. void show_stack() {
  19.     for (int i = 0; i <= top; i++) {
  20.         printf("%s", stack[i]);
  21.     }
  22.     printf("\n");
  23. }
  24.  
  25. int try_reduce() {
  26.     if (top >= 2 && strcmp(stack[top - 2], "(") == 0 && strcmp(stack[top - 1], "E") == 0 && strcmp(stack[top], ")") == 0) {
  27.         pop(); pop(); pop();
  28.         push("E");
  29.         return 1;
  30.     }
  31.  
  32.     if (top >= 2 && strcmp(stack[top - 2], "E") == 0 && (strcmp(stack[top - 1], "+") == 0 || strcmp(stack[top - 1], "*") == 0) && strcmp(stack[top], "E") == 0) {
  33.         pop(); pop(); pop();
  34.         push("E");
  35.         return 1;
  36.     }
  37.  
  38.     if (top != -1 && islower(stack[top][0]) && strlen(stack[top]) == 1) {
  39.         pop();
  40.         push("E");
  41.         return 1;
  42.     }
  43.  
  44.     return 0;
  45. }
  46.  
  47. int main() {
  48.     printf("Enter an Expression: ");
  49.     fgets(buffer, sizeof(buffer), stdin);
  50.     buffer[strcspn(buffer, "\n")] = 0;
  51.  
  52.     while (buffer[cursor] != '\0') {
  53.         if (isspace(buffer[cursor])) {
  54.             cursor++;
  55.             continue;
  56.         }
  57.  
  58.         char current[2] = {buffer[cursor], '\0'};
  59.         push(current);
  60.         cursor++;
  61.  
  62.         printf("Shift: ");
  63.         show_stack();
  64.  
  65.         while (try_reduce()) {
  66.             printf("Reduce: ");
  67.             show_stack();
  68.         }
  69.     }
  70.  
  71.     if (top == 0 && strcmp(stack[0], "E") == 0) {
  72.         printf("String Accepted\n");
  73.     } else {
  74.         printf("String Rejected\n");
  75.     }
  76.  
  77.     return 0;
  78. }
Success #stdin #stdout 0s 5320KB
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stdin
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(a+b)
stdout
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Enter an Expression: Shift: (
Shift: (a
Reduce: (E
Shift: (E+
Shift: (E+b
Reduce: (E+E
Reduce: (E
Shift: (E)
Reduce: E
String Accepted
https://ideone.com/KI1DIu
language:
C (gcc 8.3)
created:
2 days ago
visibility:
public

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