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  1. #include <iostream>
  2. #include <string>
  3. #include <string.h>
  4. #include <ctype.h>
  5.  
  6. bool n_expr (const char *&s, int &result);
  7. bool p_expr (const char *&s, int &result);
  8. bool o_expr (const char *&s, int &result, int eos);
  9.  
  10. bool expr (const char *&s, int &result, int eos = 0) {
  11.     while (isspace(*s)) ++s;
  12.     if (*s == eos) return false;
  13.     if (isdigit(*s)) {
  14.         if (!n_expr(s, result)) return false;
  15.     } else if (*s == '(') {
  16.         if (!p_expr(s, result)) return false;
  17.     } else return false;
  18.     while (isspace(*s)) ++s;
  19.     if (*s == eos) return true;
  20.     return o_expr(s, result, eos);
  21. }
  22.  
  23. bool n_expr (const char *&s, int &result) {
  24.     int n = 0;
  25.     while (isdigit(*s)) n = 10 * n + (*s++ - '0');
  26.     result = n;
  27.     return true;
  28. }
  29.  
  30. bool p_expr (const char *&s, int &result) {
  31.     if (expr(++s, result, ')')) {
  32.         ++s;
  33.         return true;
  34.     }
  35.     return false;
  36. }
  37.  
  38. bool o_expr (const char *&s, int &result, int eos) {
  39.     int oresult = 0;
  40.     const char *op = strchr("+-*/", *s);
  41.     if (op == 0) return false;
  42.     if (!expr(++s, oresult, eos)) return false;
  43.     switch (*op) {
  44.     case '+': result += oresult; break;
  45.     case '-': result -= oresult; break;
  46.     case '*': result *= oresult; break;
  47.     case '/': result /= oresult; break;
  48.     default: return false;
  49.     }
  50.     return true;
  51. }
  52.  
  53. int main() {
  54. 	std::string buf;
  55. 	const char *p;
  56. 	int r;
  57. 	while (std::getline(std::cin, buf)) {
  58. 		if (expr(p = buf.c_str(), r)) {
  59. 			std::cout << r << std::endl;
  60. 		} else {
  61. 			std::cout << "ERROR\n";
  62. 		}
  63. 	}
  64. 	return 0;
  65. }
Runtime error #stdin #stdout 0s 3436KB
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https://ideone.com/1D2IUk
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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