The first thing we do is store each character's frequency in an array
called freq. We can take advantage of the fact that a
char is really just a numeric value and use the character
itself as the index for its frequency (e.g. we store the frequency of
the character 'a' in freq['a'].)
#include <stdio.h>
#define SIZE 128 /* number of chars in the ASCII char set */
main()
{
int c, i;
int freq[SIZE]; /* frequencies of characters */
for (i = 0; i < SIZE; ++i)
freq[i] = 0;
while ((c = getchar()) != EOF)
++freq[c];
}
To print the histogram, we have to iterate through
freq using a for-loop; if a frequency is
greater than zero, we print the character followed by another
for-loop that prints the number of dashes that corresponds
with the character's frequency. If the character is invisible, we print
its escape sequence instead.
#include <stdio.h>
#define SIZE 128 /* number of chars in the ASCII char set */
main()
{
int c, i, j;
int freq[SIZE]; /* frequencies of characters */
for (i = 0; i < SIZE; ++i)
freq[i] = 0;
while ((c = getchar()) != EOF)
++freq[c];
/* print the histogram */
for (i = 0; i < SIZE; ++i) {
if (freq[i] > 0) {
if (i == ' ')
printf("\\ : ");
else if (i == '\n')
printf("\\n: ");
else if (i == '\t')
printf("\\t: ");
else if (i == '\\')
printf("\\\\: ");
else
printf("%2c: ", i);
for (j = 0; j < freq[i]; ++j)
putchar('-');
putchar('\n');
}
}
}
Note: we use %2c because escape sequences are two
characters long. Doing this ensures the bars align regardless of
whether invisible characters are entered or not.