如何用C语言编写简易的计算器

Question

## # 编程环境为VC6.0 和 C-Free

Answer 1

表达式计算建议看一下《数据结构》，先转换为逆波兰表达式，然后再计算。
当然用字符串匹配也是可以的，但是这样复杂度会比较高，
匹配最里面的括号有一个方法就是寻找第一个右括号，和这个右括号对应的左括号合起来就是最里面的括号。
当然我给你一个逆波兰表达式的代码吧，可以解决你的问题，有点长，300多行：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#define ElemItem    Item
#define SUCCEED     1
#define ERROR       0
#define MAXLENGTH   20
struct Item{
    int type;                   //0表示单目运算符，1表示双目运算符，2表示数字
    double num;             //如果是数字就保存在这里
    char oper[MAXLENGTH];   //如果是运算符就保存在这里
}nullItem;
typedef struct SNode{
    ElemItem data;
    SNode *next;
}*Stack;
struct QNode{
    ElemItem data;
    QNode *next;
};
struct Queue{
    QNode *front;
    QNode *rear;
};
void initStack(Stack *s){
    *s = NULL;
}
void push(Stack *s, ElemItem e){
    SNode *p = (SNode*)malloc(sizeof(SNode));
    p->data = e;
    p->next = *s;
    *s = p;
}
int pop(Stack *s, ElemItem *e = NULL){
    if(*s == NULL){
        return ERROR;
    }
    if(e != NULL){
        *e = (*s)->data;
    }
    SNode *p = *s;
    *s = (*s)->next;
    free(p);
    return SUCCEED;
}
ElemItem getSData(Stack s){
    if(s == NULL){
        return nullItem;
    }
    return s->data;
}
void initQueue(Queue *q){
    q->front = NULL;
    q->rear = NULL;
}
void in(Queue *q, ElemItem e){
    QNode* p = (QNode*)malloc(sizeof(QNode));
    p->data = e;
    p->next = NULL;
    if(q->rear != NULL){
        q->rear->next = p;
    }
    q->rear = p;
    if(q->front == NULL){
        q->front = p;
    }
}
int out(Queue *q, ElemItem *e){
    if(q->front == NULL){
        return ERROR;
    }
    *e = q->front->data;
    QNode *p = q->front;
    q->front = q->front->next;
    free(p);
    return SUCCEED;
}
ElemItem getQData(Queue q){
    if(q.front == NULL){
        return nullItem;
    }
    return q.front->data;
}
int getPriority(char *a){
    if(strcmp(a, "+") == 0 || strcmp(a, "-") == 0)
        return 1;
    if(strcmp(a, "*") == 0 || strcmp(a, "/") == 0)
        return 2;
    if(strcmp(a, "^") == 0)
        return 3;
    if(strcmp(a, "sin") == 0 || strcmp(a, "cos") == 0 || strcmp(a, "tan") == 0 \
    || strcmp(a, "ln") == 0 || strcmp(a, "exp") == 0 \
    || strcmp(a, "arcsin") == 0 || strcmp(a, "arccos") == 0 || strcmp(a, "arctan") == 0)
        return 4;
    return -1;
}
int getCombination(char *a){    //1表示左结合，0表示右结合
    if(strcmp(a, "+") == 0 || strcmp(a, "-") == 0 || strcmp(a, "*") == 0 || strcmp(a, "/") == 0 || strcmp(a, "^") == 0)
        return 1;
    if(strcmp(a, "sin") == 0 || strcmp(a, "cos") == 0 || strcmp(a, "tan") == 0 \
    || strcmp(a, "ln") == 0 || strcmp(a, "exp") == 0 \
    || strcmp(a, "arcsin") == 0 || strcmp(a, "arccos") == 0 || strcmp(a, "arctan") == 0)
        return 0;
    return -1;
}
int getOrder(char *a){          //0表示单目，1表示双目
    if(strcmp(a, "+") == 0 || strcmp(a, "-") == 0 || strcmp(a, "*") == 0 || strcmp(a, "/") == 0 || strcmp(a, "^") == 0)
        return 1;
    if(strcmp(a, "sin") == 0 || strcmp(a, "cos") == 0 || strcmp(a, "tan") == 0 \
    || strcmp(a, "ln") == 0 || strcmp(a, "exp") == 0 \
    || strcmp(a, "arcsin") == 0 || strcmp(a, "arccos") == 0 || strcmp(a, "arctan") == 0)
        return 0;
    return -1;
}
double getResult0(char *oper, double a1){
    if(strcmp(oper, "+") == 0)
        return a1;
    if(strcmp(oper, "-") == 0)
        return -a1;
    if(strcmp(oper, "sin") == 0)
        return sin(a1);
    if(strcmp(oper, "cos") == 0)
        return cos(a1);
    if(strcmp(oper, "tan") == 0)
        return tan(a1);
    if(strcmp(oper, "ln") == 0)
        return log(a1);
    if(strcmp(oper, "exp") == 0)
        return exp(a1);
    if(strcmp(oper, "arcsin") == 0)
        return asin(a1);
    if(strcmp(oper, "arccos") == 0)
        return acos(a1);
    if(strcmp(oper, "arctan") == 0)
        return atan(a1);
    return 0;
}
double getResult1(char *oper, double a1, double a2){
    if(strcmp(oper, "+") == 0)
        return a1+a2;
    if(strcmp(oper, "-") == 0)
        return a1-a2;
    if(strcmp(oper, "*") == 0)
        return a1*a2;
    if(strcmp(oper, "/") == 0)
        return a1/a2;
    if(strcmp(oper, "^") == 0)
        return pow(a1,a2);
    return 0;
}
double calculate(char *expression){
//对表达式信息初步读取
    int length = strlen(expression);
    Queue firstExp;
    initQueue(&firstExp);
    int flag = -1;  //0表示数字，1表示运算符,2表示函数
    char tmp[MAXLENGTH] = {'\0'};
    for(int i=0; i<length; i++){
        if(expression[i] != ' '){
            if((expression[i] >= '0' && expression[i] <= '9') || expression[i] == '.'){
                if(flag == 1 || flag == 2){
                    Item item;
                    item.type = getOrder(tmp);
                    strcpy(item.oper, tmp);
                    in(&firstExp, item);
                    flag = 0;
                    tmp[0] = '\0';
                }
                if(flag == -1){
                    flag = 0;
                }
            }else{
                if(expression[i] >= 'a' && expression[i] <= 'z'){
                    if(flag == 0){
                        Item item;
                        item.type = 2;
                        item.num = strtod(tmp, NULL);
                        in(&firstExp, item);
                        flag = 2;
                        tmp[0] = '\0';
                    }else if(flag == 1){
                        Item item;
                        item.type = getOrder(tmp);
                        strcpy(item.oper, tmp);
                        in(&firstExp, item);
                        flag = 2;
                        tmp[0] = '\0';
                    }else if(flag == 2 && getOrder(tmp) != -1){
                        Item item;
                        item.type = getOrder(tmp);
                        strcpy(item.oper, tmp);
                        in(&firstExp, item);
                        tmp[0] = '\0';
                    }
                    if(flag == -1){
                        flag = 2;
                    }
                }else{
                    if(flag == 0){
                        Item item;
                        item.type = 2;
                        item.num = strtod(tmp, NULL);
                        in(&firstExp, item);
                        flag = 1;
                        tmp[0] = '\0';
                    }else if(flag == 2){
                        Item item;
                        item.type = getOrder(tmp);
                        strcpy(item.oper, tmp);
                        in(&firstExp, item);
                        flag = 1;
                        tmp[0] = '\0';
                    }else if(flag == 1){
                        Item item;
                        item.type = getOrder(tmp);
                        strcpy(item.oper, tmp);
                        in(&firstExp, item);
                        tmp[0] = '\0';
                    }
                    if(flag == -1){
                        flag = 1;
                    }
                }
            }
            int l = strlen(tmp);
            if(l < MAXLENGTH-1){
                tmp[l] = expression[i];
                tmp[l+1] = '\0';
            }
            //printf("first runing\n");
        }
    }
    if(flag == 0){
        Item item;
        item.type = 2;
        item.num = strtod(tmp, NULL);
        in(&firstExp, item);
    }else{
        Item item;
        item.type = 1;
        strcpy(item.oper, tmp);
        in(&firstExp, item);
    }
    tmp[0] = '\0';

    //printf("first end\n");
    /*Item i;
    while(out(&firstExp, &i)){
        if(i.type == 2){
            printf("%lf\n", i.num);
        }else{
            printf("%s\n", i.oper);
        }
    }*/
//生成后缀表达式
    int frontHasNum = 0;        //最开始有无数字，0表示无数字，1表示有数字，如果最开始无数字，则第一个运算符降为单目运算符
    Stack operStack;
    initStack(&operStack);
    Queue secondExp;
    initQueue(&secondExp);
    Item firstItem;
    while(out(&firstExp, &firstItem)){
        if(firstItem.type == 2){
            frontHasNum = 1;
            in(&secondExp, firstItem);
        }else{
            if(strcmp(firstItem.oper, "(") == 0){
                frontHasNum = 0;
                push(&operStack, firstItem);
            }else if(strcmp(firstItem.oper, ")") == 0){
                frontHasNum = 1;
                Item t;
                while(strcmp(getSData(operStack).oper, "(") != 0){
                    if(!pop(&operStack, &t))
                        break;
                    in(&secondExp, t);
                    //printf("second 1 while\n");
                }
                pop(&operStack);
            }else{
                Item t;
                while((getPriority(firstItem.oper) < getPriority(getSData(operStack).oper)) \
                || (getPriority(firstItem.oper)==getPriority(getSData(operStack).oper) && getCombination(getSData(operStack).oper)==1)){
                    if(!pop(&operStack, &t))
                        break;
                    in(&secondExp, t);
                    //printf("second 2 while\n");
                }
                if(frontHasNum == 0){
                    frontHasNum = 1;
                    firstItem.type = 0;
                }
                push(&operStack, firstItem);
            }
        }
        //printf("second runing\n");
    }
    while(pop(&operStack, &firstItem)){
        in(&secondExp, firstItem);
        //printf("second in runing\n");
    }

    //printf("second end\n");
    /*Item i2;
    while(out(&secondExp, &i2)){
        if(i2.type == 2){
            printf("%lf\n", i2.num);
        }else{
            printf("%s\n", i2.oper);
        }
    }*/
//计算
    Stack startCalculate;
    initStack(&startCalculate);
    Item startItem;
    while(out(&secondExp, &startItem)){
        if(startItem.type == 2){
            push(&startCalculate, startItem);
        }else{
            if(startItem.type == 0){
                Item a;
                pop(&startCalculate, &a);
                a.num = getResult0(startItem.oper, a.num);
                push(&startCalculate, a);
            }else if(startItem.type == 1){
                Item a1,a2;
                pop(&startCalculate, &a2);
                pop(&startCalculate, &a1);
                Item a;
                a.type = 2;
                a.num = getResult1(startItem.oper, a1.num, a2.num);
                push(&startCalculate, a);
            }
        }
        //printf("calculating\n");
    }

    Item result;
    pop(&startCalculate, &result);
    return result.num;
}
int main(int argc, char *argv[]){
    char exp[200] = {'\0'};
    if(argc != 2){
        printf("输入表达式：\n");
        //scanf("%s", exp);
        gets(exp);
    }else{
        strcpy(exp, argv[1]);
    }
    printf("计算结果为：%lf\n", calculate(exp));
    return 0;
}

运行后直接输入算式就可以了。