string_operations

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>

int i = 0, j = 0, k=0;
char c;

int length(char str[]);
void reverse(char str[]);
//void search(char str[]);
void copy(char str2[], char str1[]);
int compare(char str1[], char str2[]);
void concat(char str1[], char str2[]);
int palindrome(char str[]);
int frequency(char str[]);

int main(){
	char a[15], b[15];
	int res, ch;
	do{
		printf("\n1. Length of a string");
		printf("\n2. Reverse a string");
		printf("\n3. Copy string");
		//printf("\n4. Search in a string");
		printf("\n4. Check if a string is palindrome");
		printf("\n5. Compare two strings");
		//printf("\n7. Compare two strings");
		printf("\n6. Count frequency of a character");
		printf("\n7. Exit");
		printf("\n. Enter your choice");
		scanf("%d", &ch);
		//flushall();
		switch(ch){
			case 1: 
				printf("\nEnter the string");
				scanf("%s", a);
				res = length(a);
				printf("\nLength of the string is %d", res);
				break;

			case 2:
				printf("\nEnter the string");
				scanf("%s", a);
				reverse(a);
				printf("\nReversed string is %s", a);
				break;

			case 3: copy(b,a);  //copy a in b
				printf("\nNew string b is %s", b);
				break;

			case 4: printf("\nEnter the string");
					scanf("%s", a);
					res = palindrome(a);
					if(res == 0)
						printf("\nNot palindrome");
					else
						printf("\nPalindrome");
			break;

			case 5: printf("\nEnter first string");
					scanf("%s", a);
					printf("\nEnter second string");
					scanf("%s", b);
					res = compare(a,b);
					if(res == 0)
						printf("\nBoth are same");
					else if(res > 0)
						printf("\nstring a > string b");
					else
						printf("\nstring b > string a");
					break;

			case 6: 
					printf("\nEnter the string");
					scanf("%s", a);

					res = frequency(a);
					printf("\n%c occured %d times", c, res);
					break;

			default: printf("\nInvalid entry!");
		}
	}while(ch !=7);
	return 0;
}

int length(char str[]){
	while(str[i] != '\0')
		i++;
	return i;
}

void reverse(char str[]){
	char temp;
	i = j = 0;
	while(str[i] != '\0')
		i++;
	//i now contains length of the string
	i--; //as indices start from 0
	while(j<i){
		temp = str[j];
		str[j] = str[i]; // swap last and first value 
		str[i] = temp;
		j++;
		i--;
	}

}

int palindrome(char str[]){
	while(str[j]!= '\0')
		j++;
	i =0;
	while(i<j){
		if(str[i] != str[j-1])
			return 0;
		i++; //move forward
		j--; // come backward
	}
	return 1;
}

void copy(char str2[], char str1[]){
	while(str1[i] != '\0'){
		str2[i] = str1[i];
		i++;
	}
	str2[i] = '\0';
}

int compare(char str1[], char str2[]){
	i=0;
	while(str1[i] != '\0'){
		if(str1[i] > str2[i])
			return 1;
		if(str1[i] < str2[i])
			return -1;
	}
	return 0;
}
void concat(char str1[], char str2[]){
	while(str1[i] != '\0')
		i++;
	for(j=0; str2[j]!= '\0'; i++,j++)
		str1[i] = str2[j]; 
	str1[k] = '\0';
}
int frequency(char str[]){
	printf("\nEnter the character");
	scanf("%c", &c);
	int count = 0;
	for(i = 0; str[i] != '\0'; ++i)
   {
       if(str[i] == 'c')
           ++count;
   }
	return count;

}