C++ for loop that reverses the digits 10 - 99 - c++

Question

I am trying to write code that will list and reverse all digit pairs from 01 - 99. 01-09 is easy enough since you just have to multiply it by 10. I also know at least one way to reverse a given digit, I just don't know how to properly use it with a for loop.
This is what I have so far.
for ( int num99 =1 ; num99 > 0 && num99 < 100; num99 = num99+1)
{
if (num99 <10){
temp99 = num99 * 10;
cout << temp99 << endl;
}
else {
while (num99 != 0) {
remainder99 = num99 % 10;
reverse99 = (reverse99 * 10) + remainder99;
num99 = num99 / 10;
}
cout << reverse99 << endl;
}
}
Thank you for any help.

Answer 1

You have to reinitialize the values of remainder99, reverse99, temp99, num99 after you have used them.
You also have to prepend 0 to the result, when you reverse 10, 20, 30 etc... to get 01, 02, 03 etc...
After making the necessary changes, your program will look like this.
#include<iostream>
using namespace std;
int main(void)
{
int remainder99 = 0;
int reverse99 = 0;
int temp99 = 0;
for ( int num99 =1 ; num99 > 0 && num99 < 100; num99 = num99+1)
{
if (num99 <10){
temp99 = num99 * 10;
cout << temp99 << endl;
}
else {
temp99 = num99;
while (num99 != 0) {
remainder99 = num99 % 10;
reverse99 = (reverse99 * 10) + remainder99;
num99 = num99 / 10;
}
if(reverse99 < 10) cout << 0;
cout << reverse99 << endl;
reverse99 = 0;
remainder99 = 0;
num99 = temp99;
}
}
return 0;
}
Output is:
10
20
30
40
50
60
70
80
90
01
11
21
31
41
51
61
71
81
91
02
12
22
32
42
52
62
72
82
92
03
13
23
33
43
53
63
73
83
93
04
14
24
34
44
54
64
74
84
94
05
15
25
35
45
55
65
75
85
95
06
16
26
36
46
56
66
76
86
96
07
17
27
37
47
57
67
77
87
97
08
18
28
38
48
58
68
78
88
98
09
19
29
39
49
59
69
79
89
99

Answer 2

What you are trying to do is trying to operate over the loop variable, which causes unexpected results. Instead, separate your loop variable and your num99 variable like this:
for (int i = 1; i < 100; i++) {
int num99 = i;
if (num99 < 10) {
temp99 = num99 * 10;
cout << temp99 << endl;
} else {
remainder99 = num99 % 10;
num99 = num99 / 10;
if (remainder99 == 0) {
cout<<"0"<<num99<<endl;
} else {
reverse99 = remainder99 * 10 + num99;
cout << reverse99 << endl;
}
}
}
I have also taken the liberty of assuming that when you reverse the two digit numbers like 10, 20, etc, you want the output to be 01, 02, like that, if that is not what is expected by you, you can remove the if condition.

Answer 3

There are lot of issues with mentioned code like
Here reverse99 * 10 what is initial value of reverse99 ? Assign it as 0.
Here num99 = num99 / 10; you are modifying original num99 which outer loop variable, instead of this assign num99 to some temporary variable & do operation with that temporary variable.
Sample Code
int main(void) {
int temp99 = 0,remainder99 = 0, reverse99 = 0/* must initialize with 0 */ ;
for ( int num99 =1 ; num99 > 0 && num99 < 100; num99 += 1) {
if (num99 <10){
temp99 = num99 * 10;
std::cout << num99 << std::endl;
}
else {
reverse99 = 0;/*make it as 0 again for every iteration */
temp99 = num99; /* assign loop variable to temp99 & do the operation with that */
while (temp99 != 0) {
remainder99 = temp99 % 10;
reverse99 = (reverse99 * 10) + remainder99;
temp99 /= 10;
}
std::cout << reverse99 << std::endl;
}
}
return 0;
}

Answer 4

A C++11 oriented solution:
#include <vector>
#include <iostream>
#include <numeric>
#include <algorithm>
int main()
{
std::vector<int> in(99);
std::iota(in.begin(), in.end(), 1);
std::for_each(in.begin(), in.end(), [](int& i)
{
i = (i % 10)*10 + (i / 10);
}
);
for (const auto& val : in)
{
std::string out = std::to_string(in);
if (out.size() == 1)
{
out = '0' + out;
}
std::cout << out << std::endl;
}
return 0;
}