C控制语句：分支与跳转

//统计字符、单词和行
#include<stdio.h>
#include<ctype.h>        //为isspace()提供函数原型
#include<stdbool.h>        //为bool、true和flase提供定义
#define  STOP  ‘|‘
int main(void)
{
    char c;                //读入字符
    char prev;            //前一个读入字符
    long n_chars=0L;    //字符数
    int n_lines=0;        //行数
    int n_words=0;        //单词数
    int p_lines=0;        //不完整的行数
    bool inword=false;    //如果C在一个单词中，则 inword等于true

    printf("Enter text to be analyzed(| to terminate):\n");
    prev=‘\n‘;            //用于识别完整的行
    while((c=getchar())!=STOP)
    {
        n_chars++;        //统计字符
        if(c==‘\n‘)
            n_lines++;    //统计行
        if(!isspace(c)&&!=inword)
        {
            inword=true;    //开始一个新单词
            n_words++;        //统计单词
        }
        if(isspace(c)&&inword)
            inword=false;    //到达单词的结尾
        prev=c;                //保存字符值
    }

    if(prev!=‘\n‘)
        p_lines=true;
    printf("characters=%ld,words=%d,lines=%d,",
            n_chars,n_words,n_lines);
    printf("partial lines=%d\n",p_lines);
    return 0;
}

求出温度低于零度的天数的百分比
//求出温度低于零度的天数的百分比
#include<stdio.h>
int main(void)
{
    const int FREEZING=0;
    float temperature;
    int cold_days=0;
    int all_days=0;//初始化天气温度输入总天数

    printf("Enter the list of daily low temperatures.\n");
    printf("Use Celsius,and enter q to quit.\n");
    while(scanf("%f",&temperature)==1)//有正确输入则进入循环
    {
        all_days++;
        if(temperature<FREEZING)
            cold_days++;//零度以下温度天数计数器
    }
    if(all_days!=0)
        printf("%d days total:%.1f%% were below freezing.\n",
            all_days,100.0*(float)cold_days/all_days);
    if(all_days==0)
        printf("No data entered!\n");
    return 0;
}

改变输入，只保留其中的空格
//改变输入，只保留其中的空格
//getchar()和putchar()只对字符起作用，不需要格式说明符
#include<stdio.h>
#define   SPACE  ‘ ‘
int main(void)
{
    char ch;

    ch=getchar();        //读取一个字符
    while(ch!=‘\n‘)        //当一行未结束时
    {
        if(ch==SPACE)   //空格的时候不变
            putchar(ch);//不改变这个字符
        else
            putchar(ch+1);    //改变其他字符
            ch=getchar();//获取下一个字符
    }
        
    putchar(ch);        //打印换行字符
    return 0;
}

//使用条件运算符
#include<stdio.h>
#define CONVERACE  200
int main(void)
{
    int sq_feet;
    int cans;

    printf("Enter number of square feet to be painted:\n");
    while(scanf("%d",&sq_feet)==1)
    {
        cans=sq_feet/CONVERACE;
        cans+=((sq_feet%CONVERACE==0))?0:1;
        printf("You need %d %s of print.\n",cans,cans==1?"can":"cans");
        printf("Enter next value(q to quit):\n");
    }
    return 0;
}

//使用continue跳过部分循环
//程序接受输入一系列数字，然后输出最小值和最大值
#include<stdio.h>
int main(void)
{
    const float MIN=0.0f;
    const float MAX=100.0f;

    float score;
    float total=0.0f;
    int n=0;
    float min=MAX;
    float max=MIN;

    printf("Enter the first score(q to quit):");
    while(scanf("%f",&score)==1)
    {
        if(score<MIN||score>MAX)
        {
            printf("%0.1f is an invalid value,try again:",score);
            continue;
        }
        printf("Accepting %0.1f:\n",score);
        min=(score<min)?score:min;
        max=(score>max)?score:max;
        total+=score;
        n++;
        printf("Enter next score (q to quit):");
    }
    if(n>0)
    {
        printf("Average of %d scores is %0.1f.\n",n,total/n);
        printf("Low=%0.1f,high=%0.1f\n",min,max);
    }
    else
        printf("No valid scores were entered.\n");
    return 0;
}

使用break语句跳出循环
//使用break语句跳出循环
#include<stdio.h>
int main(void)
{
    float length,width;

    printf("Enter the length of the rectangle:\n");
    while(scanf("%f",&length)==1)
    {
        printf("Length=%0.2f:\n",length);
        printf("Enter its width:\n");
        if(scanf("%f",&width)!=1)//导致程序终止包含它的循环，并进行程序的下一阶段
            break;
        printf("Width=%0.2f:\n",width);
        printf("Area=%0.2f:\n",length*width);
        printf("Enter the length of the rectangle:\n");
    }
    printf("Done.\n");
    return 0;
}