递归下降语法分析

  1 # include <stdio.h>

  2 # include <string.h>

  3 # include <stdlib.h>

  4 int E();

  5 int G();

  6 int T();

  7 int Ss();

  8 int F();

  9 char a[52];

 10 int total=0;

 11 int i=0;

 12 int temp=1;

 13 int main()

 14 {

 15     gets(a);

 16     int f;

 17     

 18     f=E();

 19     if(f==0)

 20         return 0;

 21     if(a[i] == '#')

 22         printf("accept\n");

 23     else

 24     {

 25         printf("error\n");

 26         return 0;

 27     }

 28 }

 29 int E()

 30 {

 31     int f,t;

 32     printf("%d E-->TG\n",total++);

 33     f=T();

 34     if(!f)

 35         return 0;

 36     t=G();

 37     if(!t)

 38         return 0;

 39     else

 40         return 1;

 41     

 42 }

 43 int G()

 44 {

 45     int f,t;

 46     if(a[i] == '+')

 47     {

 48         i++;

 49         printf("%d G-->+TG\n",total++);

 50         f=T();

 51         if(!f)

 52             return 0;

 53         t=G();

 54         if(!t)

 55             return 0;

 56         else

 57             return 1;

 58     }

 59     else 

 60     {

 61         printf("%d G-->&\n",total++);

 62         return 1;

 63     }

 64 

 65 }

 66 int T()

 67 {

 68     int f,t;

 69     printf("%d T-->FS\n",total++);

 70     f=F();

 71     if(!f)

 72         return 0;

 73     t=Ss();

 74     if(!t)

 75         return 0;

 76     else

 77         return 1;

 78 }

 79 int Ss()

 80 {

 81     int f,t;

 82     if(a[i] == '*')

 83     {

 84         i++;

 85         printf("%d S-->*FS\n",total++);

 86         f=F();

 87         if(!f)

 88             return 0;

 89         t=Ss();

 90         if(!t)

 91             return 0;

 92         else

 93             return 1;

 94     }

 95     else

 96     {

 97         printf("%d S-->&\n",total++);

 98         return 1;

 99     }

100 

101 }

102 int F()

103 {

104     int f,t;

105     if(a[i] == '(')

106     {

107         i++;

108         printf("%d F-->(E)\n",total++);

109         f=E();

110         if(!f)

111             return 0;

112         if(a[i] == ')')

113             i++;

114         else

115         {

116             printf("error\n");

117             return 0;

118         }

119     }

120     else if(a[i] == 'i')

121     {

122         i++;

123         printf("%d F-->i\n",total++);

124     }

125     return 1;

126 }