Program showing various operations on string(functions implemented
with pointers).
functions implemented:

(1) Reversing a string
(2) Palindrome
(3) Copy
(4) String comparison
(5) Searching a string(substring)

 #include  
 #include  
 #include  
 #include  
 /*function prototypes*/  
 void reverse(char *a);  
 int palindrome(char *a);  
 void copy(char *b,char *a);  
 int compare(char *a,char *b);  
 void search(char *a,char *b);  
 void main()  
 { char a[100],b[100];  
 int result,op;  
 clrscr();  
 do  
 { /* display the menu */  
 printf("\n1)Reverse the Given String");  
 printf("\n2)Check for palindrome");  
 printf("\n3)Copy");  
 printf("\n4)String Comparison");  
 printf("\n5)String Searching(substring)");  
 printf("\n6)Quit");  
 printf("\n\nEnter Your Choice:");  
 scanf("%d",&op);  
 flushall();  
 switch(op)  
 {  
 case 1: printf("\n Enter a String:");  
 gets(a);  
 reverse(a);  
 printf("\n Result=%s",a);  
 printf("\n\n press a Character !!!!!!");  
 getch();  
 break;  
 case 2: printf("\n Enter a String:");  
 gets(a);  
 result=palindrome(a);  
 if(result==0)  
 printf("\nNot a palindrome");  
 else  
 printf("\nA palindrome");  
 printf("\n\n press a Character !!!!!!");  
 getch();  
 break;  
 case 3: printf("\n Enter a String:");  
 gets(a);  
 copy(b,a);  
 printf("\nResult=%s",b);  
 printf("\n\n press a Character !!!!!!");  
 getch();  
 break;  
 case 4: printf("\n Enter 1st string:");  
 gets(a);  
 printf("\n Enter 2nd string:");  
 gets(b);  
 result=compare(a,b);  
 if(result==0)  
 printf("\nboth are same");  
 else  
 if(result>0)  
 printf("\n1st>2nd");  
 else  
 printf("\n1st<2nd");  
 printf("\n\n press a Character !!!!!!");  
 getch();  
 break;  
 case 5: printf("\n Enter 1st string:");  
 gets(a);  
 printf("\n Enter 2nd string:");  
 gets(b);  
 search(a,b);  
 printf("\n\n press a Character !!!!!!");  
 getch();break;  
 }  
 }while(op!=6);  
 }  
 void reverse(char *a)  
 { char *p,*q;  
 char temp;  
 /* Algorithm used is an inplace Algorithm  
 1. q is postioned on the last character  
 2. p is postioned on the first character  
 3. *p is interchanged with *q  
 4. p is increased by 1 and q is decremented by 1  
 5. if p"""  
 */  
 p=q=a;  
 while(*q!='\0')  
 q++;  
 /* q is on the null character*/  
 q--;  
 while(p /* Algorith used  
 1. q is positioned on the last character  
 2. p is positioned on the first character  
 3. if *p != *q then it is not a palindrome,return(0)  
 4. p is increased by 1 and q is decremented by 1  
 5. if p"""  
 6. string is a palindrome , return(1)  
 */  
 p=q=a;  
 while(*q!='\0')  
 q++;  
 /* q is on the null character*/  
 q--;/*q is on the last character*/  
 while(p /* Algorithm  
 1.both the strings are compared,character by character  
 from the beginning  
 2.on first point of mismatch:  
 a.if(*a>*b) then a>b  
 b.if(*a  
 3. if both the strings end together then they are eqaul  
 */  
 while(*a!='\0')  
 {  
 if(*a > *b)  
 return(1);  
 if(*a < *b)  
 return(-1);  
 a++;b++;  
 }  
 return(0);  
 }  
 void search(char *a ,char *b)  
 { int lena,lenb;  
 char *i,*j,*k;  
 /*Algorithm  
 1. lenb=length of string b[],lena=length of a[]  
 string a[] is scanned using the pointer i from location  
 0 to length of a[]-lenb+1  
 2. string b[] is matched in string a[] from the position i  
 */  
 for(lena=0;*(a+lena)!='\0';lena++)  
 ;  
 for(lenb=0;*(b+lenb)!='\0';lenb++)  
 ;  
 /* searching */  
 for(i=a;i<=a+lena-lenb+1;i++)  
 { k=i;  
 for(j=b;*k==*j&& *j!='\0';j++,k++)  
 ;  
 if(*j=='\0')  
 printf("\nstring found at location:%d",i-a+1);  
 }  
 }  
 ""  

String operations with pointers Output

1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:1

Enter a String:India

Result=aidnI

press a Character !!!!!!
1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:2

Enter a String:India

Not a palindrome

press a Character !!!!!!
1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:2

Enter a String:madam

A palindrome

press a Character !!!!!!

1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:3

Enter a String:Asia

Result=Asia

press a Character !!!!!!
1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:4

Enter 1st string:India

Enter 2nd string:Asia

1st>2nd

press a Character !!!!!!
1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:5

Enter 1st string:Pacific

Enter 2nd string:c

string found at location:3
string found at location:7

press a Character !!!!!!
1)Reverse the Given String
2)Check for palindrome
3)Copy
4)String Comparison
5)String Searching(substring)
6)Quit

Enter Your Choice:6