going reverse in a for loop?

Question

Hello there, Basically i got this for loop and i want the number inputed (eg. 123) to be printed out in reverse, so "321". so far it works fine and prints out the correct order when the for loop is

for(i = 0; i<len ; i++)

but i get an error when i try to print it in reverse?. Whats going wrong?

#include <stdio.h>
#include <string.h>
void cnvrter(char *number);

int main(){
    char number[80];
    printf("enter a number ");
    gets(number);
    cnvrter(number);

    return 0;
}

void cnvrter(char *number){
    char tmp[80];
    int i = 0,len = 0;
    int cnvrtd_digit = 0;
    len = strlen(number);
    printf("\nsize of input %d\n",len);
    for(i = len; i>len ; i--){
        if ( ( number[i] >= '0' ) && ( number[i]<='9' ) ){
            tmp[0] = number[i];
            sscanf(tmp,"%d",&cnvrtd_digit);

        }
        printf("%d\n",cnvrtd_digit);
    }
}

Answer 1

You never advance the index on tmp, and you never null-terminate it.

Answer 2

Look at your for loop again:

for(i = len; i>len ; i--){

You're doing i=len, and then testing for i>len -- unless something goes seriously wrong in the assignment, that's never going to be true...

By the way, though it's not related, you shouldn't be using gets, even in a program like this that you never intend to put to serious use.

Answer 3

I think that`s wrong:

for(i = len; i>len ; i--){

Maybe like:

for(i = len-1; i>=0; i--){

Answer 4

You don't need an explicit for-loop to reverse a string in C++. You could use std::reverse() or str.rbegin(), str.rend().

// -*- coding: utf-8 -*-
// $ g++ *.cc && (echo 'abc1d23e->١<-_ f999fff' | ./a.out)
#include <algorithm>  // remove_copy_if
#include <functional> // not1
#include <iostream>
#include <iterator>   // ostream_iterator
#include <string>

int main() {
  using namespace std;

  cout << "enter a number " << flush;               // print prompt
  string str; cin >> str;                           // read until first space
  cout << "\nsize of input " << str.size() << endl;

  remove_copy_if(
      str.rbegin(), str.rend(),                     // traverse in reverse order
      ostream_iterator<string::value_type>(cout, "\n"), // copy to stdout
                                                        // separated by newline
      not1(ptr_fun((int (*)(int))isdigit)));        // remove non-digits
}

Run it:

$ g++ *.cc && (echo 'abc1d23e->١<-_ f999fff' | ./a.out)
enter a number 
size of input 15
3
2
1