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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. void push(const char *s) {
  11.     if (top < 99)
  12.         strcpy(stack[++top], s);
  13.     else
  14.         printf("Stack overflow!\n");
  15. }
  16.  
  17. void pop() {
  18.     if (top >= 0)
  19.         top--;
  20. }
  21.  
  22. void printStack() {
  23.     for (int i = 0; i <= top; i++) printf("%s", stack[i]);
  24.     printf("\n");
  25. }
  26.  
  27. void skipWhitespace() {
  28.     while (input[pos] == ' ') pos++;
  29. }
  30.  
  31. int reduce() {
  32.     if (top >= 2 &&
  33.         strcmp(stack[top - 2], "E") == 0 &&
  34.         strcmp(stack[top - 1], "+") == 0 &&
  35.         strcmp(stack[top], "E") == 0) {
  36.         pop(); pop(); pop();
  37.         push("E");
  38.         return 1;
  39.     }
  40.  
  41.     if (top >= 2 &&
  42.         strcmp(stack[top - 2], "E") == 0 &&
  43.         strcmp(stack[top - 1], "*") == 0 &&
  44.         strcmp(stack[top], "E") == 0) {
  45.         pop(); pop(); pop();
  46.         push("E");
  47.         return 1;
  48.     }
  49.  
  50.     if (top >= 2 &&
  51.         strcmp(stack[top - 2], "(") == 0 &&
  52.         strcmp(stack[top - 1], "E") == 0 &&
  53.         strcmp(stack[top], ")") == 0) {
  54.         pop(); pop(); pop();
  55.         push("E");
  56.         return 1;
  57.     }
  58.  
  59.     if (top >= 0 && islower(stack[top][0]) && stack[top][1] == '\0') {
  60.         pop();
  61.         push("E");
  62.         return 1;
  63.     }
  64.  
  65.     return 0;
  66. }
  67.  
  68. int main() {
  69.     printf("Enter an Expression: ");
  70.     fgets(input, sizeof(input), stdin);
  71.     input[strcspn(input, "\n")] = '\0';
  72.  
  73.     while (input[pos] != '\0') {
  74.         skipWhitespace();
  75.         if (input[pos] == '\0') break;
  76.  
  77.         char temp[2] = {input[pos], '\0'};
  78.  
  79.         if (islower(input[pos]) || input[pos] == '+' || input[pos] == '*' || input[pos] == '(' || input[pos] == ')') {
  80.             push(temp);
  81.             pos++;
  82.  
  83.             printf("Shift: ");
  84.             printStack();
  85.  
  86.             while (reduce()) {
  87.                 printf("Reduce: ");
  88.                 printStack();
  89.             }
  90.         } else {
  91.             printf("Invalid character: %c\n", input[pos]);
  92.             return 1;
  93.         }
  94.     }
  95.  
  96.     if (top == 0 && strcmp(stack[0], "E") == 0)
  97.         printf("String Accepted\n");
  98.     else
  99.         printf("String Rejected\n");
  100.  
  101.     return 0;
  102. }
  103.  
Success #stdin #stdout 0s 5312KB
comments (?)
stdin
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Standard input is empty
stdout
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Enter an Expression: String Rejected
https://ideone.com/N5ft5e
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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