singly circular linked list in c

1:  #include <stdio.h>  
2:  #include <stdlib.h>  
3:  #include <dos.h>  
4:  #include <malloc.h>  
5:  struct sclink  
6:  {  
7:       int data;  
8:       struct sclink*next;  
9:  };  
10:  typedef struct sclink LINK;  
11:  LINK*head=NULL;  
12:  void addnode()  
13:  {  
14:    LINK*th;  
15:    char ch;  
16:    if(head==NULL)  
17:    {  
18:          head=(LINK*)malloc(sizeof(LINK));  
19:          printf("\nEnter data: ");  
20:          scanf("%d",&head->data);  
21:          head->next=head;  
22:          printf("Do You want to continue Y?");  
23:        fflush(stdin);  
24:        ch=getchar();  
25:        if(ch!='Y'&&ch!='y')       
26:         return;         
27:    }  
28:    th=head;  
29:    while(th->next!=head)  
30:    th=th->next;  
31:    do  
32:    {  
33:          th->next=(LINK*)malloc(sizeof(LINK));  
34:          th=th->next;  
35:          printf("Enter data:");  
36:          scanf("%d",&th->data);  
37:          th->next=head;  
38:          printf("Do you want to continue Y?:");  
39:          fflush(stdin);  
40:          ch=getchar();  
41:    }while(ch=='Y'||ch=='y');  
42:  }  
43:  void displaynode()  
44:  {  
45:       LINK*th;  
46:       if(head==NULL)  
47:       {  
48:            printf("LIST IS EMPTY\n");  
49:            system("PAUSE");  
50:            return;  
51:       }  
52:       th=head;  
53:       do  
54:       {  
55:         printf("node data:%d\n",th->data);  
56:         th=th->next;  
57:       }while(th!=head);  
58:       system("PAUSE");  
59:       return;       
60:  }  
61:  int nodecount()  
62:  {  
63:    int count=0;  
64:    LINK*th;  
65:    if(head==NULL)  
66:         return count;  
67:    th=head;  
68:    do  
69:    {  
70:          ++count;  
71:          th=th->next;  
72:    }while(th!=head);  
73:    return count;  
74:  }  
75:  void insertnode()  
76:  {  
77:       LINK*th1,*th2;  
78:       int i,nl,lp;  
79:       if(head==NULL)  
80:       {  
81:            printf("LIST IS EMPTY\n");  
82:            system("PAUSE");  
83:            return;  
84:       }  
85:       printf("Enter Link position: ");  
86:       scanf("%d",&lp);  
87:       nl=nodecount();  
88:       if(lp<1||lp>nl)  
89:       {  
90:            printf("Invalid link position\n");  
91:            system("PAUSE");  
92:            return;  
93:       }  
94:       if(lp==1)  
95:       {  
96:         th1=(LINK*)malloc(sizeof(LINK));  
97:         printf("Enter data:");  
98:         scanf("%d",&th1->data);  
99:         th1->next=head;  
100:         th2=head;  
101:         while(th2->next!=head)  
102:         th2=th2->next;  
103:         head=th1;  
104:         th2->next=head;  
105:         return;  
106:       }  
107:       th1=head;  
108:       for(i=1; i<lp-1; i++)  
109:        th1=th1->next;  
110:    th2=(LINK*)malloc(sizeof(LINK));  
111:         printf("\nEnter data: ");  
112:         scanf("%d",&th2->data);  
113:         th2->next=th1->next;  
114:         th1->next=th2;  
115:         return;  
116:  }  
117:  void deletenode()  
118:  {  
119:       LINK*th1,*th2;  
120:       int i,nl,lp;  
121:       if(head==NULL)  
122:       {  
123:            printf("LIST IS EMPTY\n");  
124:            system("PAUSE");  
125:            return;  
126:       }  
127:       printf("Enter Link position: ");  
128:       scanf("%d",&lp);  
129:       nl=nodecount();  
130:       if(lp<1||lp>nl)  
131:       {  
132:            printf("Invalid link position\n");  
133:            system("PAUSE");  
134:            return;  
135:       }  
136:       if(nl==1)  
137:       {  
138:            free(head);  
139:            head=NULL;  
140:            return;  
141:       }  
142:       if(lp==1)  
143:       {  
144:            th1=head;  
145:            head=head->next; //head=th1->next;  
146:            th1->next=NULL;  
147:            th2=head;  
148:            while(th2->next!=th1)  
149:             th2=th2->next;  
150:            th2->next=head;  
151:            free(th1);  
152:            th1=th2=NULL;  
153:            return;  
154:       }  
155:       th1=head;  
156:       for(i=1; i<lp-1; i++)  
157:        th1=th1->next;  
158:        th2=th1->next;  
159:        th1->next=th2->next;  
160:        th2->next=NULL;  
161:        free(th2);  
162:    return;  
163:  }  
164:  void updatenode()  
165:  {  
166:       int nl,lp,i;  
167:       LINK*th;  
168:       if(head==NULL)  
169:       {  
170:            printf("LIST IS EMPTY:\n");  
171:            system("PAUSE");  
172:            return;  
173:       }  
174:       printf("Enter Link position: ");  
175:       scanf("%d",&lp);  
176:       nl=nodecount();  
177:       if(lp<1||lp>nl)  
178:       {  
179:            printf("invalid link position\n");  
180:            system("PAUSE");  
181:            return;  
182:       }  
183:       if(lp==1)  
184:       {  
185:            printf("\nEnter New Data: ");  
186:            scanf("%d",&head->data);  
187:            return;  
188:       }  
189:       th=head;  
190:       for(i=1; i<lp; i++)  
191:        th=th->next;  
192:       printf("\nEnter New Data: ");  
193:       scanf("%d",&th->data);  
194:       return;  
195:  }  
196:  void reversenode()  
197:  {  
198:       LINK*prev=head;  
199:       LINK*current=head->next;  
200:       LINK*next;  
201:       int nl;  
202:       if(head==NULL)  
203:    {  
204:       printf("LIST IS EMPTY\n");  
205:       system("PAUSE");  
206:       return;  
207:    }  
208:    nl=nodecount();  
209:    if(nl==1)  
210:    {  
211:          printf("Can't do Reverse:\n");  
212:          system("PAUSE");  
213:          return;  
214:    }  
215:    while(current!=head)  
216:       {  
217:            next=current->next;  
218:            current->next=prev;  
219:            prev=current;  
220:            current=next;  
221:       }  
222:       head->next=prev;  
223:       head=prev;  
224:  }  
225:  int main()  
226:  {  
227:       int option;  
228:       while(1)  
229:       {  
230:            system("CLS");  
231:            printf("\n1 FOR ADD NODE: ");  
232:            printf("\n2 FOR DISPLAY : ");  
233:            printf("\n3 FOR NODE COUNT: ");  
234:            printf("\n4 FOR INSERT NODE: ");  
235:            printf("\n5 FOR DELETE NODE: ");  
236:            printf("\n6 FOR UPDATE NODE: ");  
237:            printf("\n7 FOR REVERSE NODE: ");  
238:            printf("\n8 FOR EXIT....: ");  
239:            scanf("%d",&option);  
240:            switch(option)  
241:            {  
242:                 case 1: addnode();  
243:                           break;  
244:                 case 2: displaynode();  
245:                           break;  
246:                 case 3:   
247:                 printf("Node count=%d\n",nodecount());  
248:                     system("PAUSE");  
249:                           break;  
250:                 case 4: insertnode();  
251:                           break;  
252:                 case 5: deletenode();  
253:                           break;  
254:                 case 6: updatenode();  
255:                           break;  
256:                 case 7: reversenode();  
257:                           break;  
258:                 case 8: free(head);  
259:                      return EXIT_SUCCESS;  
260:            }//switch  
261:       }//while  
262:  }//main