棧在表達(dá)式計(jì)算過(guò)程中的應(yīng)用 ：建立操作數(shù)棧和運(yùn)算符棧。運(yùn)算符有優(yōu)先級(jí)。
規(guī)則：
自左至右掃描表達(dá)式，凡是遇到操作數(shù)一律進(jìn)操作數(shù)棧。
當(dāng)遇到運(yùn)算符時(shí)，如果它的優(yōu)先級(jí)比運(yùn)算符棧棧頂元素的優(yōu)先級(jí)高就進(jìn)棧。反之，取出棧頂運(yùn)算符和操作數(shù)棧棧頂?shù)倪B續(xù)兩個(gè)操作數(shù)進(jìn)行運(yùn)算，并將結(jié)果存入操作數(shù)棧，然后繼續(xù)比較該運(yùn)算符與棧頂運(yùn)算符的優(yōu)先級(jí)。
左括號(hào)一律進(jìn)運(yùn)算符棧，右括號(hào)一律不進(jìn)運(yùn)算符棧，取出運(yùn)算符棧頂運(yùn)算符和操作數(shù)棧頂?shù)膬蓚€(gè)操作數(shù)進(jìn)行運(yùn)算，并將結(jié)果壓入操作數(shù)棧，直到取出左括號(hào)為止。

#include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX 100enum link{PUSH, PUSH_NO};typedef struct // 運(yùn)算數(shù) {int num[MAX];int top; }OP_num;typedef struct // 運(yùn)算符 {char str[MAX];int top; }OP_ch;// 運(yùn)算數(shù)置空棧 void SETNULL_num (OP_num* s) {s->top = -1; }// 運(yùn)算符置空棧 void SETNULL_ch (OP_ch* s) {s->top = -1; }// 判斷是否是數(shù)字，是返回1 不是返回0 int is_num (char ch) {if (ch >= '0' && ch <= '9'){return 1;}else{return 0;} } // 數(shù)字入棧 int PUSH_num (OP_num *s, int data) {if ((MAX - 1) == s->top){return 0;}else{ s->num[++s->top] = data;} }// 運(yùn)算符入棧 int PUSH_ch (OP_ch* s, char ch) {if ((MAX - 1) == s->top){return 0;}else{s->str[++s->top] = ch;} }// 判斷是否將運(yùn)算符入棧 int jud (OP_ch* s, char ch) {if (-1 == s->top) // 判斷是否是空棧{return PUSH;}else{switch (s->str[s->top]) // 根據(jù)棧頂運(yùn)算判斷是否進(jìn)棧{case '+': // 當(dāng)棧頂是'+-'時(shí)，只有‘+-）’不進(jìn)棧case '-':{if (ch == '+' || ch == '-' || ch == ')'){return PUSH_NO;}else{return PUSH;}break;}case '*':case '/':{if ('(' == ch){return PUSH;}else{return PUSH_NO;}break;}case '(':{return PUSH;break;}}} }// 數(shù)字出棧 int Pop_num (OP_num* s) {return (s->num[s->top--]); }// 運(yùn)算符出棧 void Pop_ch (OP_ch* s) {s->top--; }// 進(jìn)行運(yùn)算 void operate (OP_ch* s_ch, OP_num* s_sum) {int a = Pop_num(s_sum); // 取第一個(gè)數(shù)int b = Pop_num(s_sum); // 取第二個(gè)數(shù)int result;// 根據(jù)當(dāng)前運(yùn)算符棧頂?shù)姆?hào)來(lái)判斷進(jìn)行何種運(yùn)算switch (s_ch->str[s_ch->top]){case '+':result = a + b;break;case '-':result = b - a;break;case '*':result = a * b;break;case '/':result = b / a;break;} PUSH_num (s_sum, result); // 將運(yùn)算結(jié)果入棧 }int main() {OP_num sdata;OP_ch soper;SETNULL_num (&sdata);SETNULL_ch (&soper);int i = 0, len_str, t;char str[MAX];char str_num[MAX]; // 存放要轉(zhuǎn)化的數(shù)字gets (str); // 輸入表達(dá)式len_str = strlen (str); // 獲取表達(dá)式長(zhǎng)度while (str[i] != '\0') // 遍歷表達(dá)式{if (is_num(str[i])) // 判斷是否是數(shù)字{t = 0;while (is_num(str[i])){str_num[t++] = str[i++];//將表達(dá)式中的數(shù)字進(jìn)行保存，用于轉(zhuǎn)化為對(duì)應(yīng)的整形數(shù)}str_num[t] = '\0';PUSH_num (&sdata, atoi(str_num));// 遇到算數(shù)符號(hào)的時(shí)候讓符號(hào)前面的數(shù)進(jìn)棧}else{if (PUSH == jud(&soper, str[i])){PUSH_ch (&soper, str[i]);}else{if (str[i] != ')') // ')'不讓其入棧所以單獨(dú)列出來(lái)討論{operate (&soper, &sdata); // 進(jìn)行一次運(yùn)算并一處棧頂運(yùn)算符Pop_ch(&soper); // 符號(hào)出棧PUSH_ch (&soper, str[i]); // 進(jìn)行壓棧// 相當(dāng)于用當(dāng)前的運(yùn)算符替換了剛才棧頂?shù)倪\(yùn)算符號(hào)}else // 遇到')'// 不斷取字符運(yùn)算 知道遇到 ')'{do{operate (&soper, &sdata);Pop_ch (&soper);}while (soper.str[soper.top] != '(');Pop_ch (&soper);// 將‘（’彈出棧空間}}i++;}}while (soper.top != -1){operate (&soper, &sdata);Pop_ch (&soper);}printf ("%d\n", sdata.num[sdata.top]);return 0; } 創(chuàng)作挑戰(zhàn)賽新人創(chuàng)作獎(jiǎng)勵(lì)來(lái)咯，堅(jiān)持創(chuàng)作打卡瓜分現(xiàn)金大獎(jiǎng)

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