Answer to Exercise 1-14, page 24
Solution by Richard Heathfield
Write a program to print a histogram of the frequencies of different characters in its input.
Naturally, I've gone for a vertical orientation to match exercise 13. I had some difficulty ensuring that the printing of the X-axis didn't involve cheating. I wanted to display each character if possible, but that would have meant using isprint(), which we haven't yet met. So I decided to display the value of the character instead. (The results below show the output on an ASCII system - naturally, a run on an EBCDIC machine would give different numbers.) I had to jump through a few hoops to avoid using the % operator which, again, we haven't yet met at this point in the text.
#include <stdio.h>
/* NUM_CHARS should really be CHAR_MAX but K&R haven't covered that at this stage in the book */
#define NUM_CHARS 256
int main(void)
{
int c;
long freqarr[NUM_CHARS + 1];
long thisval = 0;
long maxval = 0;
int thisidx = 0;
for(thisidx = 0; thisidx <= NUM_CHARS; thisidx++)
{
freqarr[thisidx] = 0;
}
while((c = getchar()) != EOF)
{
if(c < NUM_CHARS)
{
thisval = ++freqarr[c];
if(thisval > maxval)
{
maxval = thisval;
}
}
else
{
thisval = ++freqarr[NUM_CHARS];
if(thisval > maxval)
{
maxval = thisval;
}
}
}
for(thisval = maxval; thisval > 0; thisval--)
{
printf("%4d |", thisval);
for(thisidx = 0; thisidx <= NUM_CHARS; thisidx++)
{
if(freqarr[thisidx] >= thisval)
{
printf("*");
}
else if(freqarr[thisidx] > 0)
{
printf(" ");
}
}
printf("\n");
}
printf(" +");
for(thisidx = 0; thisidx <= NUM_CHARS; thisidx++)
{
if(freqarr[thisidx] > 0)
{
printf("-");
}
}
printf("\n ");
for(thisidx = 0; thisidx < NUM_CHARS; thisidx++)
{
if(freqarr[thisidx] > 0)
{
printf("%d", thisidx / 100);
}
}
printf("\n ");
for(thisidx = 0; thisidx < NUM_CHARS; thisidx++)
{
if(freqarr[thisidx] > 0)
{
printf("%d", (thisidx - (100 * (thisidx / 100))) / 10 );
}
}
printf("\n ");
for(thisidx = 0; thisidx < NUM_CHARS; thisidx++)
{
if(freqarr[thisidx] > 0)
{
printf("%d", thisidx - (10 * (thisidx / 10)));
}
}
if(freqarr[NUM_CHARS] > 0)
{
printf(">%d\n", NUM_CHARS);
}
printf("\n");
return 0;
}
Here's the output of the program when given its own source as input:
474 | *
473 | *
472 | *
471 | *
470 | *
469 | *
468 | *
467 | *
466 | *
465 | *
464 | *
463 | *
462 | *
461 | *
460 | *
459 | *
458 | *
457 | *
456 | *
455 | *
454 | *
453 | *
452 | *
451 | *
450 | *
449 | *
448 | *
447 | *
446 | *
445 | *
444 | *
443 | *
442 | *
441 | *
440 | *
439 | *
438 | *
437 | *
436 | *
435 | *
434 | *
433 | *
432 | *
431 | *
430 | *
429 | *
428 | *
427 | *
426 | *
425 | *
424 | *
423 | *
422 | *
421 | *
420 | *
419 | *
418 | *
417 | *
416 | *
415 | *
414 | *
413 | *
412 | *
411 | *
410 | *
409 | *
408 | *
407 | *
406 | *
405 | *
404 | *
403 | *
402 | *
401 | *
400 | *
399 | *
398 | *
397 | *
396 | *
395 | *
394 | *
393 | *
392 | *
391 | *
390 | *
389 | *
388 | *
387 | *
386 | *
385 | *
384 | *
383 | *
382 | *
381 | *
380 | *
379 | *
378 | *
377 | *
376 | *
375 | *
374 | *
373 | *
372 | *
371 | *
370 | *
369 | *
368 | *
367 | *
366 | *
365 | *
364 | *
363 | *
362 | *
361 | *
360 | *
359 | *
358 | *
357 | *
356 | *
355 | *
354 | *
353 | *
352 | *
351 | *
350 | *
349 | *
348 | *
347 | *
346 | *
345 | *
344 | *
343 | *
342 | *
341 | *
340 | *
339 | *
338 | *
337 | *
336 | *
335 | *
334 | *
333 | *
332 | *
331 | *
330 | *
329 | *
328 | *
327 | *
326 | *
325 | *
324 | *
323 | *
322 | *
321 | *
320 | *
319 | *
318 | *
317 | *
316 | *
315 | *
314 | *
313 | *
312 | *
311 | *
310 | *
309 | *
308 | *
307 | *
306 | *
305 | *
304 | *
303 | *
302 | *
301 | *
300 | *
299 | *
298 | *
297 | *
296 | *
295 | *
294 | *
293 | *
292 | *
291 | *
290 | *
289 | *
288 | *
287 | *
286 | *
285 | *
284 | *
283 | *
282 | *
281 | *
280 | *
279 | *
278 | *
277 | *
276 | *
275 | *
274 | *
273 | *
272 | *
271 | *
270 | *
269 | *
268 | *
267 | *
266 | *
265 | *
264 | *
263 | *
262 | *
261 | *
260 | *
259 | *
258 | *
257 | *
256 | *
255 | *
254 | *
253 | *
252 | *
251 | *
250 | *
249 | *
248 | *
247 | *
246 | *
245 | *
244 | *
243 | *
242 | *
241 | *
240 | *
239 | *
238 | *
237 | *
236 | *
235 | *
234 | *
233 | *
232 | *
231 | *
230 | *
229 | *
228 | *
227 | *
226 | *
225 | *
224 | *
223 | *
222 | *
221 | *
220 | *
219 | *
218 | *
217 | *
216 | *
215 | *
214 | *
213 | *
212 | *
211 | *
210 | *
209 | *
208 | *
207 | *
206 | *
205 | *
204 | *
203 | *
202 | *
201 | *
200 | *
199 | *
198 | *
197 | *
196 | *
195 | *
194 | *
193 | *
192 | *
191 | *
190 | *
189 | *
188 | *
187 | *
186 | *
185 | *
184 | *
183 | *
182 | *
181 | *
180 | *
179 | *
178 | *
177 | *
176 | *
175 | *
174 | *
173 | *
172 | *
171 | *
170 | *
169 | *
168 | *
167 | *
166 | *
165 | *
164 | *
163 | *
162 | *
161 | *
160 | *
159 | *
158 | *
157 | *
156 | *
155 | *
154 | *
153 | *
152 | *
151 | *
150 | *
149 | *
148 | *
147 | *
146 | *
145 | *
144 | *
143 | *
142 | *
141 | *
140 | *
139 | *
138 | *
137 | *
136 | *
135 | *
134 | *
133 | *
132 | *
131 | *
130 | *
129 | *
128 | *
127 | *
126 | *
125 | *
124 | *
123 | *
122 | *
121 | *
120 | *
119 | *
118 | *
117 | *
116 | *
115 | *
114 | *
113 | *
112 | *
111 | *
110 | *
109 | * *
108 | * *
107 | * *
106 | * *
105 | * *
104 | * *
103 | * *
102 | * *
101 | * *
100 | * *
99 | * *
98 | * *
97 |** *
96 |** *
95 |** *
94 |** *
93 |** *
92 |** *
91 |** *
90 |** *
89 |** *
88 |** *
87 |** *
86 |** *
85 |** *
84 |** *
83 |** *
82 |** *
81 |** *
80 |** *
79 |** *
78 |** *
77 |** *
76 |** *
75 |** *
74 |** *
73 |** *
72 |** *
71 |** * *
70 |** * *
69 |** * *
68 |** * *
67 |** * *
66 |** * *
65 |** * *
64 |** * *
63 |** * *
62 |** * *
61 |** * *
60 |** * *
59 |** * * *
58 |** * * *
57 |** * * *
56 |** * * *
55 |** * * *
54 |** * * *
53 |** * * *
52 |** * * *
51 |** ** * *
50 |** ** * *
49 |** ** ***
48 |** ** ***
47 |** ** ***
46 |** ** ***
45 |** ** ***
44 |** ** ***
43 |** * ** ***
42 |** * * * ** ***
41 |** * * * ** ***
40 |** ** * * * ** ***
39 |** ** * * * * ** ***
38 |** ** * * * * ** ***
37 |** ** * * * * ** *** *
36 |** ** * * * * ** *** *
35 |** ** * * * * ** *** *
34 |** ** * * * * ** *** *
33 |** ** * * * * ** *** *
32 |** ** * * * * ** * *** *
31 |** ** * * * * ** * *** *
30 |** ** * * * * ** * *** *
29 |** ** * * * * ** * *** *
28 |** * ** * * *** ** * * *** *
27 |** * ** * * * *** ** * * *** *
26 |** * ** * * * *** ** * * *** *
25 |** * ** * * * *** ** * * *** *
24 |** * ** * * * *** ** * * *** *
23 |** * ** * * * *** ** * * *** *
22 |** * ** * * * *** ** * * *** *
21 |** * ** * * * * *** ** * * *** * *
20 |** * ** * * * * *** ** * * *** * * * *
19 |** * ** * * * * *** ** * * *** * * * *
18 |** * ** * * * * * *** ** * * *** * * * *
17 |** * ** * * * * * *** ** * * *** * * * *
16 |** * ** * * * * * *** ** * ** *** * * * *
15 |** * ** * * * * * * * *** ** * ** *** * * * *
14 |** * ** * * * * ** * * * ** *** ** * *** *** * * * *
13 |** * ** * * * * ** * ** *** ** *** ** * *** *** * * * *
12 |** * ** * * * **** * ** *** ** *** ** * *** *** * * * *
11 |** * ** * * * **** * ** *** * *** *** ** * ******* * * * *
10 |** * ** * * * **** * ** *** * *** *** ** * ******* * * * *
9 |** * ** * * * **** * ** *** * *** *** ** * ******* * * * *
8 |** * ** * * ****** * ** *** * *** *** ** * ******* * * * *
7 |** * ** * ** ****** * ** *** * *** **** ** ********* * * * *
6 |** * ** * *** ****** * ** *** ***** **** ** ********* * * * *
5 |** * * ****** *** ****** * ** *** ***** ******* ********* * * * *
4 |** * * ****** *** ****** * ** *** ***** ******* *********** * * *
3 |** * * ****** *** ****** * ** *** ************* *********** * * *
2 |** *** ****** *** ****** * ** *** ************* *********** * * *
1 |**********************************************************************
+----------------------------------------------------------------------
0000000000000000000000000000000000000000000000111111111111111111111111
1333333344444444445555566666677777788889999999000000000111111111122222
0234578901234567890234901257902578923581235789012345789012345678901345
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