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  1. #include <stdio.h> 
  2. #include <stdlib.h> 
  3.  
  4. #define MAX 80
  5.  
  6. void inToPostfix(char*, char*); // 中序轉後序 
  7. int priority(char); // 運算子優先
  8. double eval(char*); 
  9. double cal(char, double, double); 
  10.  
  11. int main(void) { 
  12.     char infix[MAX] = {'\0'}; 
  13.  
  14.     printf("運算式："); 
  15.     scanf("%s", infix); 
  16.     printf("%f", eval(infix));
  17.  
  18.     return 0; 
  19. } 
  20.  
  21. void inToPostfix(char* infix, char* postfix) { 
  22.     char stack[MAX] = {'\0'};
  23.     int i, j, top;
  24.     for(i = 0, j = 0, top = 0; infix[i] != '\0'; i++) switch(infix[i]) { 
  25.         case '(':              // 運算子堆疊 
  26.             stack[++top] = infix[i]; 
  27.             break; 
  28.         case '+': case '-': case '*': case '/': 
  29.             while(priority(stack[top]) >= priority(infix[i])) { 
  30.                 postfix[j++] = stack[top--];
  31.             } 
  32.             stack[++top] = infix[i]; // 存入堆疊 
  33.             break; 
  34.         case ')': 
  35.             while(stack[top] != '(') { // 遇 ) 輸出至 ( 
  36.                 postfix[j++] = stack[top--];
  37.             } 
  38.             top--;  // 不輸出 ( 
  39.             break; 
  40.         default:  // 運算元直接輸出 
  41.             postfix[j++] = infix[i];
  42.     }
  43.     while(top > 0) { 
  44.         postfix[j++] = stack[top--];
  45.     }
  46. } 
  47.  
  48. int priority(char op) { 
  49.     switch(op) { 
  50.         case '+': case '-': return 1;
  51.         case '*': case '/': return 2;
  52.         default:            return 0;
  53.     } 
  54. } 
  55.  
  56. double eval(char* infix) {
  57.     char postfix[MAX]= {'\0'};
  58.     char opnd[2] = {'\0'};
  59.     double stack[MAX] = {0.0}; 
  60.  
  61.     inToPostfix(infix, postfix);    
  62.  
  63.     int top, i;
  64.     for(top = 0, i = 0; postfix[i] != '\0'; i++) switch(postfix[i]) { 
  65.         case '+': case '-': case '*': case '/': 
  66.             stack[top - 1] = cal(postfix[i], stack[top - 1], stack[top]); 
  67.             top--; 
  68.             break; 
  69.         default: 
  70.             opnd[0] = postfix[i];
  71.             stack[++top] = atof(opnd);
  72.     }             
  73.  
  74.     return stack[top];
  75. }
  76.  
  77. double cal(char op, double p1, double p2) { 
  78.     switch(op) { 
  79.         case '+': return p1 + p2; 
  80.         case '-': return p1 - p2; 
  81.         case '*': return p1 * p2; 
  82.         case '/': return p1 / p2; 
  83.     } 
  84. }
  85.  
Success #stdin #stdout 0.01s 5280KB
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運算式：8.000000
https://ideone.com/yZPi1Z
language:
C (gcc 8.3)
created:
10 days ago
visibility:
public

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