表达式求值c语言代码

要在C语言中实现表达式的求值，可以使用栈来辅助计算。栈的元素类型可以是运算符和运算数，使用两个栈分别存储运算符和运算数。具体的代码如下：

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int top;
    char* data;
} StackChar;

typedef struct {
    int top;
    float* data;
} StackFloat;

void initStackChar(StackChar* stack, int size) {
    stack->top = -1;
    stack->data = (char*)malloc(sizeof(char) * size);
}

void initStackFloat(StackFloat* stack, int size) {
    stack->top = -1;
    stack->data = (float*)malloc(sizeof(float) * size);
}

void pushChar(StackChar* stack, char value) {
    stack->top++;
    stack->data[stack->top] = value;
}

void pushFloat(StackFloat* stack, float value) {
    stack->top++;
    stack->data[stack->top] = value;
}

char popChar(StackChar* stack) {
    char value = stack->data[stack->top];
    stack->top--;
    return value;
}

float popFloat(StackFloat* stack) {
    float value = stack->data[stack->top];
    stack->top--;
    return value;
}

char topChar(StackChar* stack) {
    return stack->data[stack->top];
}

float topFloat(StackFloat* stack) {
    return stack->data[stack->top];
}

int isOperator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/';
}

int precedence(char op) {
    if (op == '*' || op == '/') {
        return 2;
    } else if (op == '+' || op == '-') {
        return 1;
    } else {
        return 0;
    }
}

float calculate(float a, float b, char op) {
    switch (op) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            return a / b;
        default:
            return 0;
    }
}

float evaluateExpression(char* expression) {
    int size = 100;
    StackChar operatorStack;
    StackFloat operandStack;

    initStackChar(&operatorStack, size);
    initStackFloat(&operandStack, size);

    int i = 0;
    while (expression[i] ! '#') {
        if (expression[i] == ' ') {
            i++;
            continue;
        }

        if (isOperator(expression[i])) {
            while (operatorStack.top != -1 && precedence(topChar(&operatorStack)) >= precedence(expression[i])) {
                char op = popChar(&operatorStack);
                float b = popFloat(&operandStack);
                float a = popFloat(&operandStack);
                float result = calculate(a, b, op);
                pushFloat(&operandStack, result);
            }
            pushChar(&operatorStack, expression[i]);
        } else {
            float number = 0;
            while (expression[i] >= '0' && expression[i] <= '9') {
                number = number * 10 + (expression[i] - '0');
                i++;
            }
            pushFloat(&operandStack, number);
            continue;
        }
        i++;
    }

    while (operatorStack.top != -1) {
        char op = popChar(&operatorStack);
        float b = popFloat(&operandStack);
        float a = popFloat(&operandStack);
        float result = calculate(a, b, op);
        pushFloat(&operandStack, result);
    }

    float finalResult = popFloat(&operandStack);

    free(operatorStack.data);
    free(operandStack.data);

    return finalResult;
}

int main() {
    char expression[100];
    printf("请输入以#作为结束符的表达式: ");
    gets(expression);

    float result = evaluateExpression(expression);
    printf("表达式的结果为: %.2f\n", result);

    return 0;
}

以上是一个简单的表达式求值的C语言代码。该代码使用两个栈分别存储运算符和运算数，在读取表达式时，根据运算符的优先级决定是否进行计算，并将结果压入运算数栈中。最终，栈中剩余的运算符需要依次计算，并得出最终的结果。