c语言怎么用函数使四则运算不按优先级

模拟简单运算器的工作，输入一个算式（没有空格），遇等号"="说明输入 结束，输出结果。假设计算器只能进行加、减、乘、除运算，运算数和结果都是整数，4 种运算符的优先级相同，按从左到右的顺序计算。例如，输入 1+2*10-10/2=后，输出10。试编写相应程序。其中的运算部分要求定义函数实现。

我想设四个函数让他分头进行，但是要输入啊——不会了

我小学的时候写过一个类似的，但是因为那个时候还小。写的好丑，凑合着看吧。不懂问我；
望采纳！

#include<stdio.h>
#include<conio.h>
#include<windows.h>


#define TEN 10

int ONE_H;
int area;
int OPERATION_1[TEN];
int OPERATION_2[TEN];
int OPERATION_A_YUN;
int OPERATION_B_YUN;

void Clearn();

void AREA();
void OPERATION_FOR_1();
void OPERATION_FOR_2();
void VALUATION();
void ADD();
void MINUS();
void MULTIPLY();
void DIVISION();
bool GUI();

int main() {
    printf("0");
    for (;;) {
        // 结果初始化为0
        area = 0;
        // 标志现在是 第奇次 还是第偶次运算 运算
        ONE_H = 0;
        //Clearn();
        while (1) {
            // 输出答案

            // 奇次
            if (ONE_H % 2 == 0)
                OPERATION_FOR_1();
            // 偶次
            if (ONE_H % 2 == 1)
                OPERATION_FOR_2();

            if (ONE_H == 0)
                VALUATION();
            // 加法
            ADD();
            // 减法
            MINUS();
            // 乘法
            MULTIPLY();
            // 除法
            DIVISION();
            if ( GUI() ) {
                break;
            }
            AREA();
            ONE_H++;
        }
    }
    return 0;
}

void AREA() {   //?????
    system("cls");
    printf("%d", area);
}

void OPERATION_FOR_1() {
    // 单个字符的读入 在10个字符 范围内
    for (OPERATION_A_YUN = 0; OPERATION_A_YUN < TEN; OPERATION_A_YUN++) {
        OPERATION_1[OPERATION_A_YUN] = getch();
        if (OPERATION_A_YUN == 0)
            system("cls");
        putchar(OPERATION_1[OPERATION_A_YUN]);
        // 如果输入的字符不是 数字的话就停止读入
        if (OPERATION_1[OPERATION_A_YUN] > '9' || OPERATION_1[OPERATION_A_YUN] < '0')
            break;
    }
}

void OPERATION_FOR_2() {
    for (OPERATION_B_YUN = 0; OPERATION_B_YUN < TEN; OPERATION_B_YUN++) {
        OPERATION_2[OPERATION_B_YUN] = getch();
        if (OPERATION_B_YUN == 0) system("cls");
        putchar(OPERATION_2[OPERATION_B_YUN]);
        if (OPERATION_2[OPERATION_B_YUN] > '9' || OPERATION_2[OPERATION_B_YUN] < '0') break;
    }
}

void VALUATION() {  //??OPERATION_1???????area
    int i, E_1 = 1;
    for (i = OPERATION_A_YUN - 1; i >= 0; i--) {
        area = area + (OPERATION_1[i] - '0') * E_1;
        E_1 *= 10;
    }
}

void ADD() {
    if (OPERATION_1[OPERATION_A_YUN] == '+' && ONE_H != 0 && ONE_H % 2 == 1) {
        int i, E_1 = 1;
        for (i = OPERATION_B_YUN - 1; i >= 0; i--) {
            area = area + (OPERATION_2[i] - '0') * E_1;
            E_1 *= 10;
        }
    }
    if (OPERATION_2[OPERATION_B_YUN] == '+' && ONE_H != 0 && ONE_H % 2 == 0) {
        int i, E_1 = 1;
        for (i = OPERATION_A_YUN - 1; i >= 0; i--) {
            area = area + (OPERATION_1[i] - '0') * E_1;
            E_1 *= 10;
        }
    }
}

void MINUS() {
    if (OPERATION_1[OPERATION_A_YUN] == '-' && ONE_H != 0 && ONE_H % 2 == 1) {
        int i, E_1 = 1;
        for (i = OPERATION_B_YUN - 1; i >= 0; i--) {
            area = area - (OPERATION_2[i] - '0') * E_1;
            E_1 *= 10;
        }
    }
    if (OPERATION_2[OPERATION_B_YUN] == '-' && ONE_H != 0 && ONE_H % 2 == 0) {
        int i, E_1 = 1;
        for (i = OPERATION_A_YUN - 1; i >= 0; i--) {
            area = area - (OPERATION_1[i] - '0') * E_1;
            E_1 *= 10;
        }
    }
}

void MULTIPLY() {
    if (OPERATION_1[OPERATION_A_YUN] == '*' && ONE_H != 0 && ONE_H % 2 == 1) {
        int i, E_1 = 1, mod_A = 0;
        for (i = OPERATION_B_YUN - 1; i >= 0; i--) {
            mod_A = mod_A + (OPERATION_2[i] - '0') * E_1;
            E_1 *= 10;
        }
        area *= mod_A;
    }
    if (OPERATION_2[OPERATION_B_YUN] == '*' && ONE_H != 0 && ONE_H % 2 == 0) {
        int i, E_1 = 1, mod_A = 0;
        for (i = OPERATION_A_YUN - 1; i >= 0; i--) {
            mod_A = mod_A + (OPERATION_1[i] - '0') * E_1;
            E_1 *= 10;
        }
        area *= mod_A;
    }
}

void DIVISION() {
    if (OPERATION_1[OPERATION_A_YUN] == '/' && ONE_H != 0 && ONE_H % 2 == 1) {
        int i, E_1 = 1, DIVISION_A = 0;
        for (i = OPERATION_B_YUN - 1; i >= 0; i--) {
            DIVISION_A = DIVISION_A + (OPERATION_2[i] - '0') * E_1;
            E_1 *= 10;
        }
        area /= DIVISION_A;
    }
    if (OPERATION_2[OPERATION_B_YUN] == '/' && ONE_H != 0 && ONE_H % 2 == 0) {
        int i, E_1 = 1, DIVISION_A = 0;
        for (i = OPERATION_A_YUN - 1; i >= 0; i--) {
            DIVISION_A = DIVISION_A + (OPERATION_1[i] - '0') * E_1;
            E_1 *= 10;
        }
        area /= DIVISION_A;
    }
}

bool GUI() {
    // 如果输入的是 A 的话就归零
    if (OPERATION_1[OPERATION_A_YUN] == 'a' || OPERATION_1[OPERATION_A_YUN] == 'A') {
        area = 0;
        system("cls");
        printf("%d", area);
        return true;
    }
    if (OPERATION_2[OPERATION_B_YUN] == 'a' || OPERATION_1[OPERATION_B_YUN] == 'A') {
        area = 0;
        system("cls");
        printf("%d", area);
        return true;
    }
    if (OPERATION_1[OPERATION_A_YUN] == '=' && ONE_H != 0 && ONE_H % 2 == 0) {
        system("cls");
        printf("%d", area);
        return true;
    }
    if (OPERATION_2[OPERATION_B_YUN] == '=' && ONE_H != 0 && ONE_H % 2 == 1) {
        system("cls");
        printf("%d", area);
        return true;
    }
    return false;
}

void Clearn(){
    ONE_H = 0;
    area = 0;
    for(int i = 0 ; i < TEN ; i++ ){
        OPERATION_1[i] = 0;
    }
    for(int i = 0 ; i < TEN ; i++ ){
            OPERATION_2[i] = 0;
    }
    OPERATION_A_YUN = 0;
    OPERATION_B_YUN = 0;
}