counting characters in char array

i wrote following code to count occurance of characters in given char array

#include <iostream>
#include <string>
using namespace std;
int main(){

char f[]={'a','a','b','c','c','d','d','f','e','e'};
int n=sizeof(f)/sizeof(char);
char max=f[0];
for (int i=1;i<n;i++)
{
    if(f[i]>max)
    {
        max=f[i];
    }
}

int m=(int)(max)+1;
int  *b=new int [m];

for (int i=0;i<n;i++)
{
    b[(int)(f[i])]++;
}

for (int i=0;i<m;i++)
{
    if(b[i]!=0)
    {
    cout<<(char)(i)<<" occurs  "<<b[i]<< "times "<<endl;   
    }      
}

return 0;
}

but it shows very bad result

 occurs  -842150451times
☺ oc开发者_如何学运维curs  -842150451times
☻ occurs  -842150451times
♥ occurs  -842150451times
♦ occurs  -842150451times
♣ occurs  -842150451times
♠ occurs  -842150451times
 occurs  -842150451times
 occurs  -842150451times
         occurs  -84215045

 occurs  -842150451times
♂ occurs  -842150451times
♀ occurs  -842150451times
 occurs  -842150451times
♫ occurs  -842150451times
☼ occurs  -842150451times
► occurs  -842150451times
◄ occurs  -842150451times
↕ occurs  -842150451times
‼ occurs  -842150451times
¶ occurs  -842150451times
§ occurs  -842150451times
▬ occurs  -842150451times
↨ occurs  -842150451times
↑ occurs  -842150451times
↓ occurs  -842150451times
→ occurs  -842150451times
← occurs  -842150451times
∟ occurs  -842150451times
↔ occurs  -842150451times
▲ occurs  -842150451times
▼ occurs  -842150451times
  occurs  -842150451times
! occurs  -842150451times
" occurs  -842150451times
# occurs  -842150451times
$ occurs  -842150451times
% occurs  -842150451times
& occurs  -842150451times
' occurs  -842150451times
( occurs  -842150451times
) occurs  -842150451times
* occurs  -842150451times
+ occurs  -842150451times
, occurs  -842150451times
- occurs  -842150451times
. occurs  -842150451times
/ occurs  -842150451times
0 occurs  -842150451times
1 occurs  -842150451times
2 occurs  -842150451times
3 occurs  -842150451times
4 occurs  -842150451times
5 occurs  -842150451times
6 occurs  -842150451times
7 occurs  -842150451times
8 occurs  -842150451times
9 occurs  -842150451times
: occurs  -842150451times
; occurs  -842150451times
< occurs  -842150451times
= occurs  -842150451times
> occurs  -842150451times
? occurs  -842150451times
@ occurs  -842150451times
A occurs  -842150451times
B occurs  -842150451times
C occurs  -842150451times
D occurs  -842150451times
E occurs  -842150451times
F occurs  -842150451times
G occurs  -842150451times
H occurs  -842150451times
I occurs  -842150451times
J occurs  -842150451times
K occurs  -842150451times
L occurs  -842150451times
M occurs  -842150451times
N occurs  -842150451times
O occurs  -842150451times
P occurs  -842150451times
Q occurs  -842150451times
R occurs  -842150451times
S occurs  -842150451times
T occurs  -842150451times
U occurs  -842150451times
V occurs  -842150451times
W occurs  -842150451times
X occurs  -842150451times
Y occurs  -842150451times
Z occurs  -842150451times
[ occurs  -842150451times
\ occurs  -842150451times
] occurs  -842150451times
^ occurs  -842150451times
_ occurs  -842150451times
` occurs  -842150451times
a occurs  -842150449times
b occurs  -842150450times
c occurs  -842150449times
d occurs  -842150449times
e occurs  -842150449times
f occurs  -842150450times

please help me what is wrong?

---

You have to initalize the "malloc"ed (new) area to 0, it contains garbage.

---

As others have said the mistake you did, I will give you another way of doing. Since there are 256 ASCII characters, just allocated a character array of that size.

char mapCount[256];
std::fill(mapCount, mapCount+256, 0); // std::fill is from <algorithm> header

Now as you did earlier, just traverse through the input sequence and the increase the corresponding mapCount value. i.e.,

++mapCount[(int)inputSequence[i]];

Finally output mapCount indexes whose value is greater than 0. Converting the index to char will give you the actual character. As @Kerrek SB suggested, there is a notion of key association with a value. You can use the associative container std::map for this task though.

---

Well, your b array is not initialized ...

my 2 cents

---

Allocated buffer should be initialized to zero

int *b=new int [m];
memset(b, 0, sizeof(int) * m);

---

Not sure I want to dig through this code, but since you tagged this as C++, I recommend The C++ Way of doing this:

#include <map>
#include <iostream>

std::map<char, unsigned int> histogram;

// Counting
for (char * it = f; it != f + sizeof(f); ++it)
  ++histogram[*it];

// Reporting
for (std::map<char, unsigned int>::const_iterator it = histogram.begin(); it != histogram.end(); ++it)
  std::cout << "Character '" << it->first << "' appears " << it->second << " times.\n";

There's no manual memory allocation, no forgetting to clean up, and it's fairly self-descriptive. (If the array f comes as a pointer without size information, you have to pass the size information separately and use that in place of sizeof(f).)

---

The actual "error" is that you are not initialising the memory you have allocated to zero, and new[] won't do that for you.

Aside from using new[] you are not actually writing any C++ at all, it is all C. Why not use vector? That will also initialise the values to 0 for you.

// at the top

#include <vector>

then

std::vector<int> b[m];

Finally use meaningful names for identifiers rather than single letters.

---

There's quite a few problems here:

What are you trying to do here?

char f[]={'a','a','b','c','c','d','d','f','e','e'};
int n=sizeof(f)/sizeof(char);
char max=f[0];
for (int i=1;i<n;i++)
{
    if(f[i]>max)
    {
       max=f[i];
    }
}

This code when finished will have assigned max the value of the highest character in the array, in this case e.

And here?

int m=(int)(max)+1;
//cout<<m;
int  *b=new int [m];

This code will allocate a new array of integers, of size m, which will be 'e' + 1. Almost certainly not what you want. You want this to be the length of your string (n).

As others have already stated, b will contain uninitialized values which will also cause some unwanted behavior.