I have written code to reverse a string in c... it works fine but I can't return the reversed string in the main() function.
#include<stdio.h>
main()
{
char a[17]="abcdefg";
reverse(a);
printf("\n");
system("PAUSE");
}
int reverse(char *a)
{
if(*a!='\0')
{
reverse(a+1);
}
printf("%c",*a);
}
it prints the reversed string but I want the reversed string in main(). How can I do this?
Following is one way to reverse string using recursion!
#include <stdio.h>
#include <string.h>
void rev_str_recursive(char arr[], size_t iStart, size_t iLast)
{
if( iStart < iLast )
{
//swap
char temp = arr[iStart];
arr[iStart] = arr[iLast];
arr[iLast] = temp;
rev_str_recursive(arr, ++iStart, --iLast);
}
}
void main()
{
char cArray[] = {"A quick brown fox jumps over a lazy dog"};
rev_str_recursive(cArray, 0, strlen(cArray)-1);
}
-1 in the original invocation of the function, this fails horribly when the string is empty (so strlen(cArray) is 0, so the value passed as iLast is the maximum value of size_t). You can simplify the interface by calling it as rev_str_recursive(cArray, strlen(cArray)) and arranging the recursive call as rev_str_recursive(arr+1, iLast-2); only when iLast > 2. Of course, since it is tail recursive, the code can be optimized to a loop without recursion.
You need to modify the string, i.e. the input buffer to reverse(), instead of just printing it.
Doing this recursively seems a bit obnoxious, but should of course be possible.
Basically, I guess the printing becomes an assignment, something like this:
Here is another way to reverse a string using recursion:
void reverseString(char* dest, char *src, int len) {
if (src == NULL || len == 0)
return;
reverseString(dest, src + 1, len - 1);
strncat_s(dest, len + 1, src, 1);
}
You can call like that:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define STRING "Let's try this one."
#define SIZE 20
void main() {
char* src = (char*)malloc(SIZE);
char* dest = (char*)malloc(SIZE);
strcpy_s(dest, SIZE, "");
strcpy_s(src, SIZE, STRING);
reverseString(dest, src, strlen(src));
/* Do anything with dest. */
// printf("%s\n", dest);
free(src);
free(dest);
}
This code is not executable :( You define int reverse but reverse function doesnt return any value
instead use this (using void):
#include<stdio.h>
main()
{
char a[17]="abcdefg";
reverse(a);
printf("\n");
system("PAUSE");
}
void reverse(char *a)
{
if(*a!='\0')
{
reverse(a+1);
}
printf("%c",*a);
}
a?#include <iostream>
using namespace std;
reverse( char *str)
{
if (*str!='\0')
{
reverse(str+1);
cout<<*str;
}
//cout<<*str when i am just printing here then why this is printing after one space ??
}
int main()
{
string a ;
cin>>a;
reverse(&a[0]);
return 0;
}
code indentation when answering with code snippets.a little change in Emre Can Kucukoglu's answer . . . we can eliminate strncat_s
void revstr_rec(char *sstr, char *dstr, int len)
{
int i = 0;
if((! *sstr) || (! len) )
return;
revstr_rec(sstr + 1, dstr, len - 1);
dstr[len - 1] = *sstr;
return;
}
int main()
{
char *sstr = NULL;
char *dstr = NULL;
sstr = malloc(16);
if(! sstr) {
printf("no memory . . .\n");
return 0;
}
strcpy(sstr, "hello world !");
printf("sstr: %s\n", sstr);
dstr = malloc(16);
if(! dstr) {
printf("no memory . . .\n");
return 0;
}
revstr_rec(sstr, dstr, strlen(sstr));
printf("dstr(recursive): %s\n", dstr);
free(sstr);
free(dstr);
return 0;
}
#include <stdio.h>
#define MAX 100
int main()
{
char str[MAX], *rev;
scanf("%s", str);
rev = reverse(str);
printf("The reversed string is : %s\n", rev);
return 0;
}
char *reverse(char ch[])
{
static char r[MAX];
static int i=0;
if(*ch == '\0') return "";
else
{
reverse(ch+1);
r[i++]=*ch;
}
return r;
}
A simple way with left and right index
void main()
{
char* str = (char*)malloc(strlen("somestring")+1);
strcpy(str, "somestring");
int leftIndex = 0;
int rightIndex = strlen(str) - 1;
printf("%s\n", ReverseString(str, leftIndex, rightIndex));
free(str);
}
char* ReverseString(char* str, int leftIndex, int rightIndex)
{
if (leftIndex == rightIndex || leftIndex == (rightIndex +1)) {
return str;
}
// flip letters
char leftLetter = *(str + leftIndex);
char rightLetter = *(str + rightIndex);
*(str + leftIndex) = rightLetter;
*(str + rightIndex) = leftLetter;
return ReverseString(str, leftIndex+1, rightIndex -1);
}
use sprintf it will print your reversed string into buffer.
#include<stdio.h>
char *b;
main()
{
char a[17]="abcdefg";
char buffer[17];
buffer[0]= '\0';
b = buffer;
reverse(a);
printf("%s\n",buffer);
}
int reverse(char *a)
{
if(*a!='\0')
{
reverse(a+1);
sprintf(b,"%c",*a);
b++;
}
}
char buffer[17]. Also: buffer is not an lvalue, so buffer++; is not possible.void palindromo(char *s)
{
if(s[0] != '\0'){
palindromo(s+1);
printf("%c", s[0]);
}
}
This is a small recursive function who print the string inverted.
#include<stdio.h>
#include<string.h>
void rev(char *);
int main()
{
char s[]="Hello";
printf("\n%s",s);
rev(s);
printf("\n%s",s);
return 0;
}
void rev(char *s)
{
static int i=0;
static int j=0;
if(j==0) //since static variable can be intitialized
{ //only with a constant literal,to store
j=strlen(s)-1; //length-1 in 1st function call, we can use
} //this trick.(condition satisfied only in 1st
//function call)
if(i<j)
{
char temp;
temp=s[i];
s[i]=s[j]; //Analogous to for(i=0,j=l-1;i<j;i++,j--)
s[j]=temp; // { //swap code }
i++;
j--;
rev(s);
}
}
static variables to record state is not using recursion correctly. You may as well have written a loop and avoided a possible race condition.
#include<stdio.h>
void reverse(char *a);
main()
{
char a[17]="abcdefg";
reverse(a);
printf("\n");
system("PAUSE");
}
void reverse(char *a)
{
if(*a!='\0')
{
reverse(a+1);
}
printf("%c",*a);
}
int reverse()function should at least return an int.