Program for String operations without library functions - DFS

/*Program for String operations without library functions */
/* Program details:
   Program showing various operations on string without library functions
   functions implemented:
   (1) Length of a string
   (2) Reversing a string
   (3) Palindrome
   (4) Copy
   (5) String comparison
   (6) String concatenations
   (7) Searching a string
   (8) Counting of Words,Characters and Special characters
 */
 
#include <stdio.h>
#include<conio.h>
#include<ctype.h>
#include<stdlib.h>
/*function prototypes*/
int length(char a[]);
void reverse(char a[]);
int palindrome(char a[]);
void copy(char a[],char b[]);
int compare(char a[],char b[]);
void concat(char a[],char b[]);
void search(char a[],char b[]);
void count(char a[]);

void main()
  { char a[100],b[100];
    int result,op;
    clrscr();
    do
      {               /* display the menu */
     printf("\n1)length of a string");
     printf("\n2)Reverse the Given String");
     printf("\n3)Check for palindrome");
     printf("\n4)Copy");
     printf("\n5)String Comparison");
     printf("\n6)String Concatenation");
     printf("\n7)String Searching");
     printf("\n8)Counting of Words,Characters & Special Characters");
     printf("\n9)Quit");
     printf("\n\nEnter Your Choice:");
     scanf("%d",&op);
     flushall();
     switch(op)
      { case 1: printf("\n Enter a String:");
            gets(a);
            result=length(a);
            printf("\n Length of %s=%d",a,result);
            printf("\n\n press a Character !!!!!!");
            getch();
            break;

        case 2: printf("\n Enter a String:");
            gets(a);
            reverse(a);
            printf("\n Result=%s",a);
            printf("\n\n press a Character !!!!!!");
            getch();
            break;
         case 3: 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 4: printf("\n Enter a String:");
            gets(a);
            copy(b,a);
            printf("\nResult=%s",b);
            printf("\n\n press a Character !!!!!!");
            getch();
            break;
        case 5: 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 6: printf("\n Enter 1st string:");
            gets(a);
            printf("\n Enter 2nd string:");
            gets(b);
            concat(a,b);
            printf("\nresult=%s",a);
            printf("\n\n press a Character !!!!!!");
            getch();break;
        case 7: 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;
        case 8: printf("\n Enter a string:");
            gets(a);
            count(a);
            printf("\n\n press a Character !!!!!!");
            getch();break;
        default : printf("\n A wrong Choice:");break;
      }

       }while(op!=9);
  }

int length(char a[])
  { int i=0;
    /* sting is scanned from beginning and until reaches the '\0'
       character
    i will give length of the string
    function returns length of the string
    */

    while(a[i] !='\0')
      i++;
    return(i);
  }
void reverse(char a[])
   { int i,j;
     char temp;
     /* Algorithm used is an inplace Algorithm
       1. j is postioned on the last character
       2. i is postioned on the first character
       3. a[i] is interchanged with a[j]
       4. i is increased by 1 and j is decremented by 1
       5. if i<j then goto step 3
      */
      i=j=0;
      while(a[j]!='\0')
       j++;
      /* j is on the null character*/
      j--;
      while(i<j)
       { temp=a[i]; a[i]=a[j];a[j]=temp;
     i++;j--;
       }
     }
int palindrome(char a[])
  { int i,j;
   /* Algorith used
      1. j is positioned on the last character
      2. i is positioned on the first character
      3. if a[i] != a[j] then it is not a palindrome,return(0)
      4. i is increased by 1 and j is decremented by 1
      5. if i<j then goto step 3
      6. string is a palindrome , return(1)
  */

     i=j=0;
      while(a[j]!='\0')
       j++;
      /* j is on the null character*/
      j--;/*j is on the last character*/
      while(i<j)
       { if(a[i]!=a[j])
      return(0);
     i++;j--;
       }
      return(1);
     }
  void copy(char b[],char a[])
     { int i=0;
       while(a[i]!='\0')
    { b[i]=a[i];
      i++;
    }
       b[i]='\0';
     }

  int compare(char a[],char b[])
     { int i;
       /* Algorithm
      1.both the strings are compared,character by character
        from the beginning
      2.on first point of mismatch:
         a.if(a[i]>b[i]) then a>b
         b.if(a[i]<b[i]) then a<b
      3. if both the strings end together then they are eqaul
       */
     i=0;
     while(a[i]!='\0')
      { if(a[i] > b[i])
     return(1);
    if(a[i] < b[i])
     return(-1);
    i++;
      }
      return(0);
    }
 void concat(char a[],char b[])
   { int i,j;
    /* Algorithm:
       1. i is position on null character in string a[]
       2. string b[] is appended at the end of,variable j is used
     */
    i=0;
    while(a[i]!='\0')
     i++;
    for(j=0;b[j]!='\0';i++,j++)
      a[i]=b[j];
    a[i]='\0';
  }
void search(char a[] ,char b[])
  { int i,j,lena,lenb;
    /*Algorithm
      1. lenb=length of string b[],lena=length of a[]
    string a[] is scanned using the variable 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=0;i<=lena-lenb+1;i++)
    {
    for(j=0;a[i+j]==b[j]&&b[j]!='\0';j++);
    if(b[j]=='\0')
      printf("\nstring found at location:%d",i+1);
    }
  }
 void count(char a[])
  { int words=0,characters=0,spchar=0,i;
    /*algorith
      1. function is isalnum() chaecks whether the current character
     is an alphabet or a digit
      2. if the current character is an alphanumeric and previous
     charater is not an alphanumeric then it is a word
      3. a word can start from beginning
     */
    for(i=0;a[i]!='\0';i++)
     { if(isalnum(a[i]) && (i==0 || !isalnum(a[i-1])))
     words++;
       characters++;
       if(!isalnum(a[i]) && !isspace(a[i]))
     spchar++;
    }
    printf("\n no of characters=%d",characters);
    printf("\n no of special characters=%d",spchar);
    printf("\n no of words=%d",words);
  }