中缀表达式求值c语言

中缀表达式求值可以通过将中缀表达式转换为后缀表达式，然后再对后缀表达式进行求值来实现。以下是一个简单的中缀表达式求值的示例程序： ```c #include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> #define STACK_SIZE 100 typedef struct { double data[STACK_SIZE]; int top; } Stack; void initStack(Stack* s) { s->top = -1; } int isStackEmpty(Stack* s) { return s->top == -1; } int isStackFull(Stack* s) { return s->top == STACK_SIZE - 1; } void push(Stack* s, double data) { if (isStackFull(s)) { fprintf(stderr, "Stack overflow.\n"); exit(EXIT_FAILURE); } s->data[++s->top] = data; } double pop(Stack* s) { if (isStackEmpty(s)) { fprintf(stderr, "Stack underflow.\n"); exit(EXIT_FAILURE); } return s->data[s->top--]; } int priority(char op) { switch (op) { case '+': case '-': return 1; case '*': case '/': return 2; default: return 0; } } double evaluate(double op1, char operator, double op2) { switch (operator) { case '+': return op1 + op2; case '-': return op1 - op2; case '*': return op1 * op2; case '/': return op1 / op2; default: fprintf(stderr, "Invalid operator: %c\n", operator); exit(EXIT_FAILURE); } } double evaluateInfixExpression(char* infix) { Stack operatorStack; double operandStack[STACK_SIZE]; int operandCount = 0; char* token = strtok(infix, " "); while (token != NULL) { if (isdigit(token[0])) { operandStack[operandCount++] = atof(token); } else { while (!isStackEmpty(&operatorStack) && priority(token[0]) <= priority(operatorStack.data[operatorStack.top])) { double op2 = operandStack[--operandCount]; double op1 = operandStack[--operandCount]; char operator = pop(&operatorStack); operandStack[operandCount++] = evaluate(op1, operator, op2); } push(&operatorStack, token[0]); } token = strtok(NULL, " "); } while (!isStackEmpty(&operatorStack)) { double op2 = operandStack[--operandCount]; double op1 = operandStack[--operandCount]; char operator = pop(&operatorStack); operandStack[operandCount++] = evaluate(op1, operator, op2); } return operandStack[0]; } int main() { char infix[STACK_SIZE]; printf("Enter an infix expression: "); fgets(infix, sizeof(infix), stdin); printf("Result: %f\n", evaluateInfixExpression(infix)); return 0; } ``` 该程序使用两个栈，一个用于存储操作符，另一个用于存储操作数。它首先将中缀表达式字符串分解成单词，然后扫描每个单词，如果它是一个操作数，则将其推入操作数栈，否则将其与操作符栈的栈顶元素进行比较。如果其优先级高于操作符栈的栈顶元素，则将其推入操作符栈，否则将操作符栈的栈顶元素弹出，与两个操作数栈的栈顶元素进行操作并将结果推入操作数栈。最后，当操作符栈为空时，操作数栈的栈顶元素即为表达式的值。