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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <ctype.h>
  4.  
  5. char input[100];
  6. int i = 0;
  7.  
  8. void shift(char c) {
  9.     printf("Shift: %c\n", c);
  10. }
  11.  
  12. void reduce(const char* rule) {
  13.     printf("Reduce: %s\n", rule);
  14. }
  15.  
  16. void parse() {
  17.     char stack[100];
  18.     int top = -1;
  19.     int len = strlen(input);
  20.  
  21.     while (i < len) {
  22.         if (isspace(input[i])) {
  23.             i++;
  24.             continue;
  25.         }
  26.  
  27.         stack[++top] = input[i];
  28.         shift(input[i]);
  29.         i++;
  30.  
  31.         int change;
  32.         do {
  33.             change = 0;
  34.  
  35.             if (top >= 2 && stack[top] == ')' && stack[top - 2] == '(' && stack[top - 1] == 'E') {
  36.                 top -= 2;
  37.                 stack[top] = 'E';
  38.                 reduce("E → (E)");
  39.                 change = 1;
  40.             }
  41.             else if (top >= 2 && stack[top] == 'E' && stack[top - 1] == '+' && stack[top - 2] == 'E') {
  42.                 top -= 2;
  43.                 stack[top] = 'E';
  44.                 reduce("E → E+E");
  45.                 change = 1;
  46.             }
  47.             else if (top >= 2 && stack[top] == 'E' && stack[top - 1] == '*' && stack[top - 2] == 'E') {
  48.                 top -= 2;
  49.                 stack[top] = 'E';
  50.                 reduce("E → E*E");
  51.                 change = 1;
  52.             }
  53.             else if (top >= 0 && islower(stack[top])) {
  54.                 stack[top] = 'E';
  55.                 reduce("E → id");
  56.                 change = 1;
  57.             }
  58.  
  59.         } while (change);
  60.     }
  61.  
  62.     if (top == 0 && stack[top] == 'E') {
  63.         printf("String Accepted \n");
  64.     }
  65.     else {
  66.         printf("String Rejected \n");
  67.     }
  68. }
  69.  
  70. int main() {
  71.     printf("Enter an Expression: ");
  72.     fgets(input, sizeof(input), stdin);
  73.     input[strcspn(input, "\n")] = 0;
  74.  
  75.     parse();
  76.  
  77.     return 0;
  78. }
Success #stdin #stdout 0.01s 5288KB
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stdin
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Standard input is empty
stdout
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Enter an Expression: String Rejected
https://ideone.com/9ZgVZa
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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