程序代码：

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

int main(int argc, char* argv[])
{
    FILE *fp;
    char buf[255];
    int counts[3], i;

    counts[0] = counts[1] = counts[2] = 0;

    if(argc == 1) {
        printf("please specify data file.\n");
        return 1;
    }

    fp = fopen(argv[1], "r");
    if(!fp) {
        printf("open file \'%s\' failed.\n", argv[1]);
        return 1;
    }

    while(fscanf(fp, "%s", buf) != EOF) {
        while(buf[strlen(buf)-1] &&
            !(('a'<=buf[strlen(buf)-1]&&buf[strlen(buf)-1]<='z')
            ||('A'<=buf[strlen(buf)-1]&&buf[strlen(buf)-1]<='Z')))
            buf[strlen(buf)-1] = 0;
        if(0 < strlen(buf) && strlen(buf) < 4)
            ++counts[strlen(buf)-1];
    }

    fclose(fp);

    for(i=0; i<3; ++i)
        printf("words with %d letters: %d\n", i+1, counts[i]);
    return 0;
}