Print a histogram

histogram.c

#include <stdio.h>
#include <string.h>
#include <limits.h>


static inline unsigned _max(unsigned values[], unsigned length) {
    unsigned max = 0;
    for(unsigned i = 0; i < length; i++) max = max > values[i] ? max : values[i];
    return max;
}


void histogram(char* keys[], unsigned values[], unsigned length, unsigned max_height) {
    unsigned max = _max(values, length);
    max_height = max_height > max ? max : max_height;
    char max_nlenbuf[15];
    
    // Needed for padding of the y-axis
    sprintf(max_nlenbuf, "%d", UINT_MAX);
    short max_nlen = strlen(max_nlenbuf);
    
    unsigned granularity = max / max_height;
    
    unsigned llens[length];
    for(unsigned i = 0; i < length; i++) llens[i] = strlen(keys[i]);
    unsigned pad = _max(llens, length) + 1;
    pad += pad % 2;

    for(unsigned step = max_height; step > 0; step--) {
        printf("%-*u:", max_nlen, (step*granularity));

        for(unsigned i = 0; i < length; i++) {
            char* bar = " ";
            if( values[i] >= step*granularity )
                bar = "█";
            
            for(unsigned _=0; _<strlen(keys[i])/2; _++) putchar(' ');
            fputs(bar, stdout);
#ifdef WIDEPRINT
            for(unsigned _=0; _<pad-1-strlen(keys[i])/2; _++) putchar(' ');
#else
            for(unsigned _=0; _<strlen(keys[i])/2+1+(strlen(keys[i])%2); _++) putchar(' ');
#endif
        }
        
        printf("\n");
    }

    printf("%-*s", max_nlen+1, "");
    for(unsigned i = 0; i < length; i++) {
#ifdef WIDEPRINT
        printf("%-*s", pad, keys[i]);
#else
        printf("%-*s", (int)strlen(keys[i])+2, keys[i]);
#endif
    }
    printf("\n");
}

histogram.h

#ifndef _H_HISTOGRAM
#define _H_HISTOGRAM

void histogram(char* keys[], unsigned values[], unsigned length, unsigned max_height);

#endif // _H_HISTOGRAM

test.c

#include "histogram.h"

int main() {
    char* keys[]      = {"foo", "bar", "baz", "quux", "biz", "booze"};
    unsigned values[] = {15,    3,     20,    32,     9,     16     };
    histogram(keys, values, sizeof(keys)/sizeof(keys[0]), 10);
}