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尚观C语言

一、格式化输入输出函数：scanf、printf

printf

int printf(const char *format, ...);

• format:"%[修饰符]格式字符"
• printf("%[修饰符]格式字符，[输出表项]")；

#include "stdio.h"
#include "stdlib.h"int main()
{printf("hello world!\n");printf("a = %d,b = %d\n",a,b);exit(0);
}

• 格式字符

• 修饰符

#include "stdio.h"
#include "stdlib.h"
#define STRSIZE 32int main()
{int i = 123;float f = 123.456;char str[STRSIZE] = "helloworld"printf("i = %4d",i);			//结果：i =   123（左补空格）printf("i = %2d",i);			//结果：i =  123（原样输出）printf("f = %f",f); 			//结果：f =  123.456001（大概范围的表示）printf("f = %8.1f",f);			//结果：f =     123.4（大概范围的表示）printf("%s\n",str);				//结果：helloworldprintf("%.5s\n",str);			//结果：helloprintf("%-10.5s[over]\n",str);	 //结果：hello     [over]printf("i = %o\n",i);			//结果：i = 173printf("i = %#o\n",i);			//结果：i = 0173printf("i = %x\n",i);			//结果：i = 78printf("i = %#x\n",i);			//结果：i = 0x78exit(0);
}

‘\n’可以刷新缓冲区

scanf

int scanf(const char *format, 地址表);

• 输入案例

#include "stdio.h"
#include "stdlib.h"int main()
{int i;float f;printf("please enter:\n");scanf("%d%f",&i,&f);//两个数据中间不要随意加东西printf("i = %d\n",i);printf("f = %f\n",f);exit(0);
}
//输入：345 38.83
//输出：   i = 345
//		  f = 38.830003

• 输入字符串
  • 用scanf输入字符串十分危险，容易出现越界现象

#include "stdio.h"
#include "stdlib.h"int main()
{int i;float f;printf("please enter:\n");scanf("%d%f",&i,&f);//两个数据中间不要随意加东西printf("i = %d\n",i);printf("f = %f\n",f);exit(0);
}

• 在while循环中scanf
  • scanf的返回值：输入成功->1 输入失败->0

#include "stdio.h"
#include "stdlib.h"int main()
{int i;float f;printf("please enter:\n");while(1){ret = scanf("%d",&i);if(ret != 1)break;printf("i = %d\n",i);}exit(0);
}

• 多个输入函数依次使用（抑制符%*）

#include "stdio.h"
#include "stdlib.h"int main()
{int i;float f;printf("please enter:\n");scanf("%d",&i);scanf("%c",&ch);	    //结果1：i = 32,ch = 10 -> 空格scanf("%*c%c",&ch); 	//结果2：i = 32,ch = 97 -> aprintf("i = %d,ch = %d\n",i,ch);exit(0);
}

二、字符输入输出函数：getchar、putchar

getchar

int getchar(void);

putchar

int putchar(int c);

#include "stdio.h"
#include "stdlib.h"int main()
{char ch;ch = getchar();putchat(ch)
}

三、字符串输入输出函数：gets()、puts

gets()

• gets是一个十分危险的函数
• 不会检查当前写缓冲区内容是否越界
• 可以使用fgets或getline函数代替

puts

#include "stdio.h"
#include "stdlib.h"
#define STRSIZE 32int main()
{char str[STRSIZE];gets(STR);puts(STR);exit(0);
}

四、练习

1）一个水分子的质量大约为3.0e-23g，一夸脱水大约有950g，要求输入水的夸克数，然后显示这么多夸克水中包含有大概多少水分子。

#include "stdio.h"
#include "stdlib.h"
#define WEIGHT 3.0e-23	//水分子的质量
#define KQ     950		//一夸脱水质量static void water(void)
{float num;//水的夸脱数float sum;//总共多少printf("please input for num：");//屏幕提示scanf("%f",&num)	//输入sum = KQ * num / WEIGHT;//数学换算printf("total is %e\n",sum);return ;
}int main()
{water();   exit(0);
}

2）从终端输入三角形的三边长求三角形的面积,要有自检部分。s=1/2(a+b+c) ,area=sqrt(s*(s-a)(s-b)(s-c))

#include "stdio.h"
#include "stdlib.h"
#include "math.h"static void area(void)
{float a,b,c;float s,area;printf("please input:");scanf("%f%f%f",&a,&b,&c);if(a+b<=c || b+c<=a || c+a<=b){fprintf(stderr,"EINVAL\n");exit(0);}s = 1.0 / 2.0 * (a + b + c);area = sqrt(s * (s - a) * (s - b) * (s - c));printf("area = %f\n",area); return ;
}int main()
{area();exit(0);
}

3）从终端输入abc的值求方程的根

• 例：求ax^2 + bx + c=0，b^2 - 4ac>0

  x1=(-b+sqrt(b^2-4ac)/2a

  x2=(-b-sqrt(b^2-4ac)/2a

#include "stdio.h"
#include "stdlib.h"
#include "math.h"static void root(void)
{float a,b,c,p,q;float disc;float x1,x2;printf("please input:");scanf("%f%f%f",&a,&b,&c);if((b*b - 4*a*c) < 0){fprintf(stderr,"EINVAL\n");exit(1);}disc = b*b-4*a*c;p = -b/2*aq = sqrt(disc)/2*a;x1 = p + q;x2 = p - q;printf("x1 = %f\nx2 = %f\n",x1,x2);return ;
}int main()
{root();exit(0);
}