Counting characters in a string or file - c

Question

I have the following code:
#include "stdafx.h"
#include "string.h"
#include "ctype.h"
/*selection sort*/
void swap(int A[], int j, int k)
{
int p = A[k];
int i;
for (i = 0; i < (k - j); i++)
{
A[k - i] = A[k - i - 1];
}
A[j] = p;
}
/*greatest number in an array*/
int max(int A[], int N, int k)
{
int max = k, i;
for (i = k; i < N; i++)
{
if (A[max] < A[i])
max = i;
}
return max;
}
int count_nonspace(const char* str)
{
int count = 0;
while(*str)
{
if(!isspace(*str++))
count++;
}
return count;
}
int _tmain(int argc, _TCHAR* argv[])
{
int a[256];
int i = 0, j = 0, count[256] = { 0 };
char string[100] = "Hello world";
for (i = 0; i < 100; i++)
{
for (j = 0; j<256; j++)
{
if (tolower(string[i]) == (j))
{
count[j]++;
}
}
}
for (j = 0; j<256; j++)
{
printf("\n%c -> %d \n", j, count[j]);
}
}
Program is calculating the number of apperances of each character in a string. Now it prints the number of apperances of all 256 characters, whereas i want it to prinf only the character with greatest number of apperances in a string. My idea was to use the selection sort method to the array with the nubmer of apperances, but this is not working, thus my question is how to printf only the character with the greatest number of apperances in the string?
If anybody would have doubts, this is NOT my homework question.
EDIT: I've just noticed that this code printf apperances of characters begining with "j" why is that?

Answer 1

I started typing this before the others showed up, so I'll post it anyway. This is probably nearly the most efficient (increasing efficiency would add some clutter) way of getting an answer, but it doesn't include code to ignore spaces, count characters without regard to case, etc (easy modifications).
most_frequent(const char * str)
{
unsigned counts[256];
unsigned char * cur;
unsigned pos, max;
/* set all counts to zero */
memset(counts, 0, sizeof(counts));
/* count occurences of each character */
for (cur = (unsigned char *)str; *cur; ++cur)
++counts[*cur];
/* find most frequent character */
for (max = 0, pos = 1; pos < 256; ++pos)
if ( counts[pos] > counts[max] )
max = pos;
printf("Character %c occurs %u times.\n", max, counts[max]);
}

Answer 2

Create an array with your char as index.
Keep incrementing the value in the array based on the characters read.
Now get the max out of the array which gives you the most occurring char in your input.
Code will look like:
#include <stdio.h>
#include<string.h>
#include<stdlib.h>
int main(void) {
char buf[100];
int i=0,max =0,t=0;
int a[256];
memset(a,0,sizeof(a));
fgets(buf,100,stdin);
buf[strlen(buf)-1] = '\0';
while(buf[i] != '\0')
{
a[(int)buf[i]]++;
i++;
}
i=0;
for(i=0;i<256;i++)
{
if(a[i] > max)
{
max = a[i];
t = i;
}
}
printf("The most occurring character is %c: Times: %d",t,max);
return 0;
}

Answer 3

Here is a solution for that, based on your own solution, and using qsort().
#include <string.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
struct Frequency
{
int character;
int count;
};
int compare(const void *const lhs, const void *const rhs)
{
return ((struct Frequency *)rhs)->count - ((struct Frequency *)lhs)->count;
}
int main(int argc, char* argv[])
{
int i = 0, j = 0;
struct Frequency count[256];
memset(&count, 0, sizeof(count));
char string[100] = "Hello world";
for (i = 0 ; i < 100 ; i++)
{
for (j = 0 ; j < 256 ; j++)
{
count[j].character = j;
if (tolower(string[i]) == j)
{
count[j].count += 1;
}
}
}
qsort(count, sizeof(count) / sizeof(*count), sizeof(*count), compare);
/* skip the '\0' which was counted many times */
if (isprint(count[1].character))
printf("\nThe most popular character is: %c\n", count[1].character);
else
printf("\nThe most popular character is: \\%03x\n", count[1].character);
for (j = 0 ; j < 256 ; j++)
{
if (isprint(count[j].character))
printf("\n%c -> %d \n", count[j].character, count[j].count);
else
printf("\n\\%03x -> %d \n", count[j].character, count[j].count);
}
}
notice that the '\0' is set for all the remainig bytes in
char string[100] = "Hello world";
so the count of '\0' will be the highest.
You could use strlen() to skip '\0', in the counting loop, but don't
for (i = 0 ; i < strlen(string) ; ++i) ...
do it this way
size_t length = strlen(string);
for (i = 0 ; i < length ; ++i) ...