题目1101：计算表达式

题目描述：: 对于一个不存在括号的表达式进行计算

输入：: 存在多种数据，每组数据一行，表达式不存在空格

输出：: 输出结果

样例输入：

6/2+3+3*4

样例输出：

18

这道题本身不难，求解有多种方法，但我却做了很多次wrong answer，一开始的代码是这样

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <algorithm>
 5  
 6  
 7 int main(int argc, char const *argv[])
 8 {
 9     bool isStart = true;
10     int temp;
11     int state = 0;
12     int ans;
13     char opt;
14     int toDeal;
15      
16     //freopen("input.txt","r",stdin);
17     while(scanf("%d%c",&toDeal,&opt) != EOF) {
18         if(isStart) {
19             temp = 1;
20             ans = 0; 
21             state = 0;
22             isStart = false;
23         }
24          
25         if(state == 0) {
26             temp = temp * toDeal;
27         }
28         else {
29             temp = temp/toDeal;
30         }
31              
32         if(opt == '+') {
33             ans = ans + temp;
34             temp = 1;
35             state = 0;
36         }
37         else if(opt == '-') {
38             ans = ans + temp;
39             temp = -1;
40             state = 0;
41         }
42         else if(opt == '*') {
43             state = 0;
44         }
45         else if(opt == '/') {
46             state = 1;
47         }
48         else {
49             ans = ans + temp;
50             printf("%d
", ans);
51             isStart = true;
52         }
53          
54     }
55     return 0;
56 }

最后发现原因是最后一行的数据opt是读不出来的，else在本地能进去，但在oj系统上就不知道了，开始修改成如下代码：

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <algorithm>
 5  
 6  
 7 int main(int argc, char const *argv[])
 8 {
 9     int temp;
10     int state = 0;
11     int ans;
12     char opt;
13     int toDeal;
14      
15     //freopen("input.txt","r",stdin);
16     while(scanf("%d",&toDeal) != EOF) {
17         temp = 1;
18         ans = 0; 
19         state = 0;
20         while(scanf("%c",&opt)!=EOF&&(opt=='+'||opt=='-'||opt=='*'||opt=='/')) {
21             if(state == 0) {
22                 temp = temp * toDeal;
23             }
24             else {
25                 temp = temp/toDeal;
26             }
27             if(opt == '+') {
28                 ans = ans + temp;
29                 temp = 1;
30                 state = 0;
31             }
32             else if(opt == '-') {
33                 ans = ans + temp;
34                 temp = -1;
35                 state = 0;
36             }
37             else if(opt == '*') {
38                 state = 0;
39             }
40             else if(opt == '/') {
41                 state = 1;
42             }
43             scanf("%d",&toDeal);
44         }
45         if(state == 0) {
46             temp = temp * toDeal;
47         }
48         else {
49             temp = temp/toDeal;
50         }
51         ans = ans + temp;
52         printf("%d
", ans);
53     }
54     return 0;
55 }

之后又做了修改

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <algorithm>
 5   
 6   
 7 int main(int argc, char const *argv[])
 8 {
 9     int temp = 1;
10     int state = 0;
11     int ans = 0;
12     char opt;
13     int toDeal;
14       
15     //freopen("input.txt","r",stdin);
16     while(scanf("%d",&toDeal) != EOF) {
17         if(state == 0) {
18             temp = temp * toDeal;
19         }
20         else {
21             temp = temp/toDeal;
22         }
23          
24         if(scanf("%c",&opt) != EOF) {
25             if(opt == '+' || opt == '-') {
26                 ans = ans + temp;
27                 temp = 1 - (opt - '+');
28                 state = 0;
29             }
30             else if(opt == '*') {
31                 state = 0;
32             }
33             else if(opt == '/') {
34                 state = 1;
35             }
36             else if(opt == '
') {
37                 ans = ans + temp;
38                 printf("%d
", ans);
39                 temp = 1;
40                 ans = 0; 
41                 state = 0;
42             }
43         }
44         else {
45             ans = ans + temp;
46             printf("%d
", ans);
47             temp = 1;
48             ans = 0; 
49             state = 0;
50         }
51     }
52     return 0;
53 }

主要的思路是把每一个乘除法作为一个temp，最后的结果是temp的累加和。