1、编写一个将输入复制到输出的程序,并将其中连续的多个空格用一个空格代替

  使用if 结构:

#include<stdio.h>
#define NONBLANK 'a';
// repalce string of blanks with a single blank
int main(void)
{
int c, lastc; // c负责记录当前输入字符的ASCII值, lastc记录前一个输入字符的ASCII值 lastc = NONBLANK; // 符号常量NONBLANK负责把lastc初始化为一个任意的非空格字符
while((c = getchar()) != EOF)
{
if(c != ' ')
putchar(c);
if(c == ' ')
if(lastc != ' ') // 输出一个或一串空格中的第一个空格
putchar(c);
lastc = c; }
return 0;
}

  使用if-else 语法结构:

#include<stdio.h>
#define NONBLANK 'a';
int main(void)
{
int c, lastc; lastc = NONBLANK;
while((c = getchar()) != EOF)
{
if(c != ' ')
putchar(c);
else if(lastc != ' ')
putchar(c);
lastc = c; }
return 0;
}

  使用逻辑或(||)操作符:

#include<stdio.h>
#define NONBLANK 'a';
int main(void)
{
int c, lastc; lastc = NONBLANK;
while((c = getchar()) != EOF)
{
if(c != ' ' || lastc != ' ')
putchar(c);
lastc = c; }
return 0;
}

2、单词计数

  要求统计行数、单词数与字符数,这里单词的定义比较宽松,它是任何其中不包含空格、制表符或换行符的字符序列。

#include<stdio.h>
#define IN 1 // inside a word
#define OUT 0 // outside a word
/* count lines, words, and characters in input */
int main(void)
{
int c, nl, nw, nc, state; state = OUT;
nl = nw = nc = 0;
while((c = getchar()) != EOF)
{
++nc;
if(c == '\n')
++nl;
if(c == ' ' || c == '\n' || c == '\t')
state = OUT;
else if(state == OUT) // 每当遇到单词的第一个字符, 它就作为一个新单词加以统计
{
state = IN;
++nw;
}
}
printf("%d %d %d\n", nl, nw, nc);
return 0;
}

Question: 如何测试程序?

 首先进行常规测试,然后测试边界条件,对于该程序而言,边界条件有:

  没有输入

  没有单词(只有换行符)

  没有单词(只有空格、制表符和换行符)

  每个单词各占一行(没有空格和制表符)

  单词出现于文本行行首

  单词出现于一串空格之后的情况

3、编写一个程序,以每行一个单词的形式打印其输入

#include<stdio.h>
#define IN 1 // inside a word
#define OUT 0 // outside a word
// print input one word per line
int main(void)
{
int c, state; // state: 记录程序的处理过程是否正处于某个单词的内部 state = OUT;
while((c = getchar()) != EOF)
{
if(c == ' ' || c == '\n' || c == '\t')
{
if(state == IN)
{
putchar('\n'); // finish the word
state = OUT;
}
}
else if(state == OUT)
{
state = IN; // beginning of word
putchar(c);
}
else
putchar(c); // inside a word
state = IN;
}
}

 下面是我画的一个流程图:

4、编写程序,打印输入中单词长度的直方图

  水平方向的直方图:

#include<stdio.h>
#define MAXHIST 15 // max length of histogram
#define MAXWORD 11 // max length of a word
#define IN 1 // inside a word
#define OUT 0 // outside a word
// print horizontal histogram
int main(void)
{
int c, i, nc, state;
int len; // length of each bar
int maxvalue; // maximum value for wl[]
int ovflow; // number of overflow words
int wl[MAXWORD]; // word length counters state = OUT;
nc = 0; // number of chars in a word
ovflow = 0; // number of words >= MAXWORD
for(i = 0; i < MAXWORD; ++i)
wl[i] = 0;
while((c = getchar()) != EOF)
{
if(c == ' ' || c == '\n' || c == '\t')
{
state = OUT;
if(nc > 0)
if(nc < MAXWORD)
++wl[nc];
else
++ovflow;
nc = 0;
}
else if(state = OUT)
{
state = IN;
nc = 1; // beginning of a new word
}
else
++nc; // inside a word
} maxvalue = 0;
for(i = 1; i < MAXWORD; ++i)
if(wl[i] > maxvalue)
maxvalue = wl[i]; for(i = 1; i < MAXWORD; ++i)
{
printf("%5d - %5d : ", i, wl[i]);
if(wl[i] > 0)
{ // 变量len根据MAZHIST和maxvalue的值计算得出的wl[i]所对应的直方图长度, 如果wl[i]大于零,就至少打印一个星号
if((len = wl[i] * MAXHIST / maxvalue) <= 0) // 收获: <= 之间不能有空格
len = 1;
}
else
len = 0;
while(len > 0)
{
putchar('*');
--len;
}
putchar('\n');
}
if(ovflow > 0)
printf("There are %d words >= %d\n", ovflow, MAXWORD);
return 0;
}

  由于垂直方向的所有直方图需要同步打印,所以垂直方向的比较难控制,注意与上述程序的区别:

#include<stdio.h>
#define MAXHIST 15 // max length of histogram
#define MAXWORD 11 // max length of a word
#define IN 1 // inside a word
#define OUT 0 // outside a word
// print horizontal histogram
int main(void)
{
int c, i, j, nc, state;
int len; // length of each bar
int maxvalue; // maximum value for wl[]
int ovflow; // number of overflow words
int wl[MAXWORD]; // word length counters state = OUT;
nc = 0; // number of chars in a word
ovflow = 0; // number of words >= MAXWORD
for(i = 0; i < MAXWORD; ++i)
wl[i] = 0;
while((c = getchar()) != EOF)
{
if(c == ' ' || c == '\n' || c == '\t')
{
state = OUT;
if(nc > 0)
if(nc < MAXWORD)
++wl[nc];
else
++ovflow;
nc = 0;
}
else if(state = OUT)
{
state = IN;
nc = 1; // beginning of a new word
}
else
++nc; // inside a word
} maxvalue = 0;
for(i = 1; i < MAXWORD; ++i)
if(wl[i] > maxvalue)
maxvalue = wl[i]; for(i = MAXHIST; i > 0; --i)
{
for(j = 1; j < MAXWORD; ++j)
if(wl[j] * MAXHIST / maxvalue >= i)
printf(" * ");
else
printf(" ");
putchar('\n');
}
for(i = 1; i < MAXWORD; ++i)
printf("%4d ", i);
putchar('\n');
for(i = 1; i < MAXWORD; ++i)
printf("%4d ", wl[i]);
putchar('\n');
if(ovflow > 0)
printf("There are %d words >= %d\n", ovflow, MAXWORD);
return 0;
}

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