#include<stdio.h>
int main(void)
{
long num;
long sum = 0L;
int status;
printf("Please enter an integer to be summed: ");
printf("(q to quit)");
while((status = scanf("%ld",&num)) == 1) //==运算符的优先级比=要高
{
sum = sum +num;
printf("Please enter next integer(q to quit):");
}
printf("Those integer sum to %ld.\n",sum);
return 0;
}
--浮点数的比较
/*
浮点数比较中只能使用大于和小于号。原因在于舍入误差可能造成两个逻辑上应该相等的数不相等了。
例如:3和1/3的乘积应该是1.0,但是您用6位小数表示1/3,乘积就是.999999而不是1
*/
#include<math.h>
#include<stdio.h>
int main(void)
{
const double ANSWER = 3.14159;
double response;
printf("What is the value of PI?\n");
scanf("%lf",&response);
while(fabs(response - ANSWER) > 0.0001)
{
printf("Try again!\n");
scanf("%lf",&response);
}
printf("Close enough!\n");
return 0;
}
//真表达式的值为1,而假表达式的值为0
#include<stdio.h>
int main(void)
{
int n = 3;
while(n)
printf("%2d is true\n",n--);
printf("%2d is false\n",n);
n = -3;
while(n)
printf("%d is true\n",n++);
printf("%2d is false\n",n);
return 0;
}
/*
C中_Bool类型在C99中提供了一个stdbool.h的头文件,可以使用bool来代替_Bool,并把true和false定义为1和0的符号常量,
包含这个头文件可以写出与c++兼容的代码,因为c++把bool、true、false定义为关键字
*/
//字符代替数字来计数
#include<stdio.h>
int main(void)
{
char ch;
for(ch = ‘a‘; ch <= ‘z‘;ch++)
printf("The ASCII value for %c is %d.\n",ch,ch);
return 0;
}
逗号运算符:
/*
1.逗号是个顺序点,逗号左边产生的所有副作用都在程序运行到逗号右边之前生效
2.整个逗号表达式的值是右边成员的值
x = (y=3,(z = ++y +2)+5); x = 11
houseprice = 249,500;
houseprice = 249 是左表达式,而500是有表达式
houseprice =(249,500);
把houseprice赋值为500,因为该值是右表达式的值
*/
//使内部循环依赖于外部循环的嵌套循环
#include<stdio.h>
int main(void)
{
const int ROWS = 6;
const int CHARS = 6;
int row;
char ch;
for(row = 0;row < ROWS;row++)
{
for(ch = (‘A‘+row); ch < (‘A‘ +CHARS);ch++)
printf("%c",ch);
printf("\n");
}
return 0;
}
数组--线性存储的一系列相同类型的值
小技巧:可以用#define指令创建一个指定数组大小的明显常量,方便以后改动。
//以下是一个计算数值的整数次幂的程序
#include<stdio.h>
double power (double n,int p);
int main(void)
{
double x,xpow;
int exp;
printf("Enter a number and the position integer power");
printf(" to which\nthe number will be raised. Enter q to quit.\n");
while(scanf("%lf%d",&x,&exp)==2)
{
xpow = power(x,exp);
printf("%.3g to the power %d is %.5g\n",x,exp,xpow);
printf("Enter next pair of numbers or q to quit.\n");
}
printf("Hope you enjoyed this power trip -- bye!\n");
return 0;
}
double power(double n,int p)
{
double pow = 1;
int i;
for(i = 1; i <= p; i++)
pow *=n;
return pow;
}