c Print out the letters, which were repeatedly in string [duplicate] - c

Question

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Bad permissions for mapped region [duplicate]
(2 answers)
Closed 9 years ago.
My function should print out letters which are more than once in string. I have no idea why I get an empty output, or my program 'stops working'.
#include <string.h>
#include <stdio.h>
void funkcja3 (char []);
int main()
{
funkcja3("napnapnaaw");
return 0;
}
void funkcja3 (char napis[])
{
int i=0,j;
for(;i<strlen(napis);i++)
{
if((napis[i]>='a')&&(napis[i]<='z'))
{
int n=0;
for(j=i+1;j<strlen(napis);j++)
{
if(napis[i]==napis[j])
{
n++;
napis[j]=' ';
}
}
if(n>0)
{
printf("%c ", napis[i]);
}
}
}
}

Answer 1

You need to pass a modifiable string:
int main()
{
char str[] = "napnapnaaw";
funkcja3(str);
return 0;
}

Answer 2

This is not a direct answer to your question, but if you just want to print out all the non-capital letters that appear more than once in a given string, then you can just use a histogram (symbol-counting) instead:
void funkcja3(char napis[])
{
int histogram['z'-'a'+1] = {0};
for (int i=0; napis[i]!=0; i++)
{
if ('a' <= napis[i] && napis[i] <= 'z')
histogram[napis[i]-'a']++;
}
for (int i=0; i<'z'-'a'+1; i++)
{
if (histogram[i] > 1)
printf("%c ",'a'+i);
}
}
BTW, histogram = the number of occurrences of each symbol in the data.

Answer 3

When I run your program on my machine (Ubuntu, gcc 4.6), I get a segmentation fault and a core dump. Giving the program and the core dump to gdb and doing a backtrace gives
$ gdb a.out core
Core was generated by `/tmp/a.out'.
Program terminated with signal 11, Segmentation fault.
#0 0x00000000004005a2 in funkcja3 (napis=0x40072c "napnapnaaw") at a.c:25
25 napis[j]=' ';
(gdb) bt
bt
#0 0x00000000004005a2 in funkcja3 (napis=0x40072c "napnapnaaw") at a.c:25
#1 0x0000000000400520 in main () at a.c:8
This hint brings me to removing line 25 and running the program again
$ a.out
n a p n a a
which shows all characters, which were repeated somewhere later in the string.

Answer 4

When you call funkcja3, you're calling it with a string literal. This string literal is at a memory location that isn't modifiable, so the call to napid[j] = ' ' should fail (and does so when I copy your example in to visual studio 2013). What you need to do is either A: use std::string (or another string implementation) or B: make a copy of the string in the function, examine it, and then delete the copy when done. Either way, you probably shouldn't be modifying the original string going in to the function. It's generally bad practice to modify objects passed in to a function unless the function absolutely has to do so.
There are some other ways of completing this task as well, such as an array of 26 shorts to hold the counts for each character. Make those counts and then print out any character that has more then 1.