c语言如何写一个eval

在C语言中编写一个简单的表达式评估器（eval）是一个相对复杂的任务，因为它需要解析和计算字符串形式的数学表达式。以下是一个简单的实现，它支持加法、减法、乘法和除法运算。

```c

include

include

include

include

define MAX_EXPR_LEN 256

// Function to evaluate the expression

double evaluate(const char expr);

// Function to check if the character is an operator

int isOperator(char c);

// Function to perform arithmetic operations

double performOperation(char op, double a, double b);

// Function to get precedence of operators

int getPrecedence(char op);

// Function to evaluate the expression using Shunting Yard algorithm

double infixToPostfix(const char infix, char postfix);

// Function to evaluate the postfix expression

double evaluatePostfix(const char postfix);

int main() {

char expression[MAX_EXPR_LEN];

printf("Enter an expression: ");

fgets(expression, MAX_EXPR_LEN, stdin);

expression[strcspn(expression, "n")] = 0; // Remove newline character

double result = evaluate(expression);

printf("Result: %fn", result);

return 0;