/*
 * ass10.c
 */
#include <stdio.h>
#define MAXLEN (1000+1)
#define CODE   128

int strLength(const char *x) { // assignment8.c
    if(*x == '\0') return 0 ;
    return 1 + strLength(x+1) ;
}

int charCount(char *x, char c){
    int i, count;
    for(i=0,count=0; x[i] != '\0'; ++i) 
        if(x[i] == c) count++;
    return count;
}

void commonChars(char *x, char *y){
     int i ;
     char present[CODE]; 

     for(i=0; i<CODE; ++i) present[i]='\0';
     for(i=0; x[i]!='\0'; ++i)
         present[(int)x[i]] = (char)1;
     for(i=0; y[i]!='\0'; ++i)
            if(present[(int)y[i]] == 1) present[(int)y[i]] = (char)2;

     for(i=0; i<CODE; ++i) 
         if(present[i] == (char)2) printf("%c ", (char)i);
}

void ror(char *x){
     char c = x[0];     
     int i, n;

     n = strLength(x);
     x[0] = x[n-1];
     for(i=n-2; i>0; --i) x[i+1]=x[i];
     x[1] = c; 
}

void rol(char *x){
     char c = x[0];
     int i, n;
     n = strLength(x);
     for(i=1; i<n; ++i) x[i-1]=x[i];
     x[n-1] = c; 
}


char *strCopy(char *x, const char *y) {
     *x = *y;
     if(*x != '\0') strCopy(x+1, y+1);
     return x;  
}

int isPrefix(const char *x, const char *y) {
    if(*y){
          if (*x == *y) return isPrefix(x+1, y+1);
          return 0; 
    } 
    return 1;
}

char *substring(char *x, const char *y) {
    if(strLength(x) < strLength(y)) return NULL ;
    if(isPrefix(x,y)) return x;
    return substring(x+1, y) ;
}

int main()
{
    char x[MAXLEN], c, y[MAXLEN], z[MAXLEN], *sP ; 

    printf("Enter the 1st string:\n") ;
    scanf("%[^\n]", x) ;
    printf("Enter a character:\n") ;
    scanf(" %c", &c) ;
    printf("%d occurrence of %c in \"%s\"\n", 
            charCount(x, c), c, x);
    printf("Enter the 2nd string:\n") ;
    scanf(" %[^\n]", y) ;
    printf("Common chars in \"%s\" and \"%s\" are: ", x, y); 
    commonChars(x,y); 
    putchar('\n');
    ror(x);
    printf("Right-rotated: \"%s\"\n", x);
    rol(x);
    printf("Left-rotated: \"%s\"\n", x);
    sP = strCopy(z, x);
    printf("sP: \"%s\", z: \"%s\"\n", sP, z);
    
    if((sP = substring(x, y)) == NULL) 
        printf("\"%s\" is not a substring of \"%s\"\n", y, x) ;
    else {
        printf("\"%s\" is a substring of \"%s\"", y, x) ;
        printf(" from index %d\n", (int)(sP-x)) ;
    }    

    return 0;
} // ass10.c