#includeint main(void){ long num; long sum = 0L; int status; printf("Please enter an integer to be summed:"); printf("(q to quit):"); status = scanf_s("%ld", &num); while (status) { sum = sum + num; printf("Please enter next integer (q to quit):"); status = scanf_s("%ld", &num); } printf("Those integers sum to %ld.\n", sum); system("pause"); return 0;}
status = scanf_s("%ld",&num);while(status=1){ /*循环行为*/ status = scanf_s("%ld",&num)}//替换代码while(scanf_s("%ld",&num)=1){ /*循环行为*/ status = scanf_s("%ld",&num)} while语句
while(expression)statement
statement部分可以是以分号结尾的简单语句，也可以是用花括号括起来的复合语句。其中，如果expression为真，执行。
在构建while循环时，必须让测试表达式的值有所变化。
while(expression)printf("sth");//如果没有花括号，只有紧跟着while后面的第一条语句才算循环other statement /*不加分号*/#includeint main(void){ int n = 0; while (n++ < 3) printf("n is %d\n", n); printf("That's all this program does.\n"); system("pause"); return 0;}/*result:n is 1n is 2n is 3That's all this program does.*//*加分号*/#include int main(void){ int n = 0; while (n++ < 3); //加分号则会让编译器认为这句号是单独的一句 printf("n is %d\n", n); printf("That's all this program does.\n"); system("pause"); return 0;}/*result:n is 4That's all this program does.*/
用关系运算符和表达式比较大小
| 运算符 | 含义 |
|---|---|
| < | 小于 |
| <= | 小于或等于 |
| == | 等于 |
| >= | 大于或等于 |
| > | 大于 |
| != | 不等于 |
注：当使用浮点数时，尽量只是用“<”或“>”，因为浮点数的舍入误差会导致在逻辑上应该相等的两数却不相等。
value_1 == value_! //判断value_1 = value_2 //赋值
#include#include int main(void){ const double ANSWER = 3.14159; double response; printf("What is the value of pi?\n"); scanf_s("%f", &response); while (fabs(response - ANSWER) > 0.0001) //fabs()函数取绝对值 { printf("Try again!\n"); scanf_s("%lf", &response); } printf("Close enough!\n"); system("pause"); return 0;}
新的_Bool类型
#includeint main(void){ long num; long sum = 0L; _Bool input_is_good; //定义Bool类型 printf("Please enter an integer to be summed"); printf("(q to quit):"); input_is_good = (scanf_s("%ld", &num) == 1); while (input_is_good) { sum = sum + num; printf("Please enter next integer(q to quit):"); input_is_good = (scanf_s("%ld", &num) == 1); } printf("Those integers sum to %ld.\n", sum); return 0;}
优先级和关系运算符
高优先级组：<、<=、>、>=
低优先级组：==、！=
不确定循环和计数循环
#includeint main(void){ const int NUMBER = 22; int count = 1; while (count <= NUMBER) { printf("Be my Valentine!\n"); count++; } system("pause"); return 0;}
for 循环
#includeint main(void){ const int NUMBER = 22; int count = 1; for (count = 1; count <= NUMBER; count++)//第一个是表达式初始化，第二个是测试条件，第三个是表达式执行更新。 printf("Be my Valentine!\n"); system("pause"); return 0;}
#includeint main(void){ char ch; for (ch = 'a'; ch <= 'z'; ch++) printf("The ASCII value for %c is %d.\n", ch, ch); system("pause"); return 0;}
可以省略一个或多个表达式（但是不能省略分号），只要在循环体中包含能结束循环的语句即可。另外，第一个表达式不一定要给变量赋初值，也可以使用printf()。但是，在执行循环体的其他部分之前，只对第一个表达式求值一次或执行一次。
#includeint main(void){ int num = 0; for (printf("Keep entering number!\n"); num != 6;) scanf_s("%d", &num); printf("That's one I want!\n"); return 0;}
其他赋值运算符
| 表达式 | 含义 |
|---|---|
| scores += 20 | scores = scores + 20 |
| dimes -= 2 | dimes = dimes - 20 |
| bunnies *= 2 | bunnies = bunnies * 20 |
| time /= 2.73 | time = time / 2.73 |
| reduce %= 3 | reduce = reduce % 3 |
逗号运算符
#includeint main(void){ const int FIRST_OZ = 46, NEXT_OZ = 20; int ounces, cost; printf("ounces cost\n"); for (ounces = 1, cost = FIRST_OZ; ounces <= 16; ounces++, cost += NEXT_OZ) //同时有多个值，且从左到右顺序执行 printf("%5d $%4.2f\n", ounces, cost / 100.0); system("pause"); return 0;}
houseprice = 249,500 //分为houseprice=249和500这两条表达式语句houseprice =(249,500)//等于houseprice=500char ch,date；//分隔符
出口条件循环：do while
#includeint main(void){ const int secret_code = 13; int code_entered; do { printf("To enter the yuan therapy clud,\n"); printf("please enter the scret code number:"); scanf_s("%d", &code_entered); } while (code_entered != secret_code); printf("Congratulation! You are cured!\n"); system("pause"); return 0;}/*dostatementwhile (expression);*/
do while循环在执行完循环体后才执行测试条件，所以至少执行循环体一次，while循环体适用于那些至少要迭代一次的循环。
嵌套循环
/*打印字母串*/#include#define ROWS 6#define CHARS 10int main(void){ int row; char ch; for (row = 0; row < ROWS; row++) { for (ch = 'A'; ch < ('A' + CHARS); ch++) printf("%c", ch); printf("\n"); } system("pause"); return 0;}
数组
float debts[n];//声明一个含有20个元素的数组debts[n]=num;//为数组元素赋值，编译器不会查找元素不在等的错误
用于识别数组元素的数字被称为下标、索引或偏移量。
/*打印字母串*/#include#define SIZE 10#define PAR 72int main(void){ int index, score[SIZE]; int sum = 0; float average; printf("Enter %d golf scores:\n", SIZE); for (index = 0; index < SIZE; index++) scanf_s("%d",&score[index]); printf("\n"); for (index = 0; index < SIZE; index++) sum += score[index]; average = (float)sum / SIZE; printf("Sum of scores = %d,average = %.2f\n", sum, average); printf("That's a handicap of %.0f.\n", average - PAR); system("pause"); return 0;}
使用函数返回值的循环
#includedouble power(double n, int p); /*C编译器运行到这里还不知道power函数是什么，所以要先声明该函数的返回值类型等，而如果该函数写在main函数的前面，则不需要在此处声明该函数*/int main(void){ double x, xpow; int exp; printf("Enter a number and the positive integer power"); printf(" to which\nthe number will be raised. Enter q"); printf(" to quit.\n"); while (scanf_s("%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"); system("pause"); return 0;}double power(double n, int p){ double pow = 1; int i; for (i = 1; i <= p; i++) pow *= n; return pow;}