字符串和格式化輸入輸出

 1 #include<stdio.h>
 2 #include<string.h>
 3 #define DENSITY 62.4
 4 
 5 int main(void)
 6 {
 7     float weight, volume;
 8     int size, letters;
 9     char name[40];//數組
10 
11     printf("Hi!What‘s your first name?");
12     gets(name);//get(sth.)取得地址
13     printf("
 
%s,What‘s your weight in pounds?\n", name);
14     scanf_s("%f", &weight);
15     size = sizeof(name);
16     letters = strlen(name);
17     volume = weight / DENSITY;
18     printf("Well,%s, your volume is %2.2f cubic feet.\n", name, volume);
19     printf("Also, your fist name has %d letters\n
 
", letters);
20     printf("We have %d bytes to store it in.\n", size);
21     return 0;
22 }

字符串

用雙引號表示，且C語言沒有專門的字符串變量類型，而是把它儲存在char數組裏面。數組的最後一個位置顯示空字符\0，用於標記字符串的結束。如 "The weather is so well!"

 1 #include<stdio.h>
 2 #define PRAISE "You are so good!"
 3 
 4 int main(void)
 5 {
 6
 
     char name[40];
 7     printf("What‘s your name?");
 8     gets(name);
 9     printf("Hello,%s,%s", name, PRAISE);
10     getchar();
11     return 0;
12 }

字符串和字符的區別

• ‘x‘是基本類型，而"x"是派生類型（char數組)；
• "x"實際上是由‘x‘和空字符兩部分組成的。

strlen函數

 1 #include<stdio.h>
 2 #define PRAISE "You are so good!"
 3 
 4 int main(void)
 5 {
 6     char name[40];
 7     printf("What‘s your name?");
 8     gets(name);
 9     printf("Hello,%s,%s", name, PRAISE);
10     printf("Your name of %zd letters occupies %zd memory cells.\n", strlen(name), sizeof name);
11     /*strlen函數給出字符數，sizeof為給出所占內存數量；但是兩者都需要使用"%zd"轉換符來打印。另外sizeof(特定量)，如sizeof(char)，而一般的類型，不使用圓括號也可以。*/
12     printf("The phraze of PRAISE has %zd letters", strlen(PRAISE));
13     printf(" and occupies %zd memory cells.\n", sizeof PRAISE);
14     getchar();
15     return 0;
16 }

這樣在程序運行時，所有的NAME將會被value替代，這樣定義的常量也稱為明示常量。

 1 #include<stdio.h>
 2 #define PI 3.14
 3 
 4 int main(void)
 5 {
 6     float area, circum, radius;
 7     printf("What‘s the radius of your pizza?\n");
 8     scanf_s("%f", &radius);
 9     area = PI * radius*radius;
10     circum = 2 * PI*radius;
11     printf("Your basic pizza parameters are as follows:\n ");
12     printf("circumference = %1.2f,area = %1.2f\n", circum, area);
13     system("pause");
14     return 0;
15 }

const限定符

const int = OLD_YEAR;//OLD_YEAR在程序裏面不可修改

明示常量

#include<limits.h>
#include<stdio.h>

int main(void)
{
    printf("%d\n", INT_MAX);
    system("pause");
    return 0;
}

limits.h

float.h

把明示常量名中的FLT分別替代成DBL和LDBL，即可分別表示double和long double類型對應的明示常量。

printf()和scanf()和*修飾符

如果不想預先指定字段寬度，希望通過程序來指定，那麽可以用*修飾符代替字段寬度；如果轉換符%*d，那麽參數列表中應包含*和d對應的值

 1 #include<stdio.h>
 2 
 3 int main(void)
 4 {
 5     unsigned width, precision;
 6     int number = 256;
 7     double weight = 242.5;
 8     printf("Enter a field width:\n");
 9     scanf_s("%d", &width);
10     printf("The number is:%*d:\n", width, number);
11     printf("Now enter a width and a precision:\n");
12     scanf_s("%d %d", &width, &precision);
13     printf("Weight = %*.*f\n", width, precision, weight);
14     printf("Done!\n");
15     system("pause");
16     return 0;
17 }

scanf()中*的用法與此不同，把*放在%和轉換符之間時，會使得scanf()跳過相應的輸入項。

 1 #include<stdio.h>
 2 int main(void)
 3 {
 4     int n;
 5     printf("Please enter three integers:\n");
 6     scanf_s("%*d %*d %d", &n);
 7     printf("The last integer was %d\n", n);
 8     system("pause");
 9     return 0;
10 }
11 
12 result:
13 Please enter three integers:
14 1 2 3
15 The last integer was 3

printf()用法提示

 1 #include<stdio.h>
 2 int main(void)
 3 {
 4     int val_1 = 12, val_2 = 345, val_3 = 1222;
 5     printf("%9d %9d %9d\n", val_1, val_2, val_3);//%nd設置字段寬度
 6     system("pause");
 7     return 0;
 8 }
 9 
10 result:
11        12       345      1222

c語言之字符串和格式化輸入輸出