计算器的实现

来源：互联网发布：执法记录仪删除数据编辑：程序博客网时间：2024/04/28 06:21

闲着无聊,写个小程序.总共两个函数,有个有点小长,不过也懒得重新封装了,也没有面向对象.注释比较详细,希望大家能看懂.

计算表达式长度限制在128位以内,支持浮点运算

#include

using namespace std;

float caculOnce(float left, char op, float right){

switch(op){

case '+':

return left + right;

case '-':

return left - right;

case '*':

return left * right;

case '/':

return left / right;

}

float caculAll(char *testCase){

int len = strlen(testCase);

float left, right, temp;//存放三个数据

left = right = temp = 0.0;

int r = 0;//存放结果

bool isLeft = true;//判断是否在读取左操作数

bool inParentheses = false;//是否在括号里

int parentheseCount = 0;//碰到的左括号个数

bool hasTemp, hasLeft, hasRight;

hasTemp = hasLeft = hasRight = false;

char stack[64];//存放括号里的内容,长度不超过20个字符

char op1 = '0',op2 = '0';//存放两个操作符

int j = 0;//标记指向stack的指针的位置

for (int i = 0; i < len; i++){

if(inParentheses){//在括号中

if(testCase[i] == '('){//是左括号

parentheseCount++;

stack[j++] = testCase[i];

}else if(testCase[i] == ')'){//是右括号

if(parentheseCount == 1){//左括号数为1

stack[j] = '\0';

right = caculAll(stack);//递归运算

inParentheses = false;

parentheseCount = j = 0;

}else{//左括号数大于1

parentheseCount --;//自减

stack[j++] = testCase[i];

}

}else{//不是括号

stack[j++] = testCase[i];//存储当前字符到stack中

}

}else if(testCase[i] >= '0' && testCase[i] <= '9'){//是数字

if(isLeft){//判断是否在操作左操作数

if(!hasLeft)

left = atof(&testCase[i]);//是，则把新数字接在左操作数尾部

hasLeft = true;

}else{//不是，则把新数字接在右操作数尾部

if(!hasRight)

right = atof(&testCase[i]);

hasRight = true;

}

}else{//不是数字

switch(testCase[i]){//判断当前符号是什么

case '*'://乘号

case '/'://除号

if(op2 == '0'){//cout<<"op2 为空"<<endl;

if(op1 == '0'){//cout<<"op1 为空"<<endl;

op1 = testCase[i];

}else{//cout<<"op1非空"<<endl;

if(op1 == '*' || op1 == '/'){//cout<<"op1为乘除"<<endl;

left = caculOnce(left, op1, right);

right = 0;

hasRight = false;

op1 = testCase[i];

}else{//cout<<"op1为加减"<<endl;

op2 = testCase[i];

temp = left;

left = right;

right = 0;

hasRight = false;

isLeft = false;

}

}else{//op2非空

if(op2 == '*' || op2 == '/'){//op2为乘除

if(op1 == '*' || op1 == '/'){//op1为乘除

left = caculOnce(temp, op1, left);

left = caculOnce(left, op2, right);

right = temp = 0;

hasTemp = hasRight = false;

op2 = '0';

op1 = testCase[i];

}else{//op1为加减

left = caculOnce(left, op2, right);

right = 0;

op2 = testCase[i];

hasRight = false;

}

}else{//op2为加减

left = caculOnce(temp, op1, left);

op1 = op2; op2 = '0';

temp = left; hasTemp = true;

left = right;

right = 0; hasRight = false;

}

isLeft = false;

break;

case '+'://加号

case '-'://减号

if(op2 == '0'){//cout<<"op2 为空"<<endl;

if(op1 == '0'){//cout<<"op1 为空"<<endl;

op1 = testCase[i];

}else{//cout<<"op1非空"<<endl;

left = caculOnce(left, op1, right);

right = 0;

hasRight = false;

op1 = testCase[i];

}

}else{//op2非空

if(op2 == '*' || op2 == '/'){//op2为乘除

if(op1 == '*' || op1 == '/'){//op1为乘除

left = caculOnce(temp, op1, left);

left = caculOnce(left, op2, right);

}else{

left = caculOnce(left, op2, right);

left = caculOnce(temp, op1, left);

}

right = temp = 0;

op2 = '0';

hasTemp = hasRight = false;

op1 = testCase[i];

}else{//op2为加减

left = caculOnce(temp, op1, left);

op1 = op2; op2 = '0';

temp = left; hasTemp = true;

left = right;

right = 0; hasRight = false;

}

isLeft = false;

break;

case '('://是左括号

parentheseCount++;//左括号数自增

inParentheses = true;

break;

default:

cout<<"invalid input!!!"<<endl;

exit(0);

}

if(i == len - 1){//最后一个字符

if(op1 != '0' && op2 != '0'){

if(op2 == '*' || op2 == '/'){//op2为乘除

if(op1 == '*' || op1 == '/'){//op1为乘除

left = caculOnce(temp, op1, left);

left = caculOnce(left, op2, right);

}else{//op1为加减

left = caculOnce(left, op2, right);

left = caculOnce(temp, op1, left);

}

}else{//op2为加减

left = caculOnce(temp, op1, left);

left = caculOnce(left, op2, right);

}

}else if(op1 != '0'){

left = caculOnce(left, op1, right);

}

cout << testCase << " = " << left << endl;//打印表达式与结果

return left;

}

int main(int argc, char *argv[]){

char ex[128];

if(argc > 1){

strcpy(ex, argv[1]);

}else{

cout << "输入计算式:";

cin >> ex;

}

cout << "the result is " << caculAll(ex) << endl;

return 0;

}

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