在C中帮助do / while和switch语句
发布时间:2020-12-16 10:29:34 所属栏目:百科 来源:网络整理
导读:尝试编译一个包含5个选项的简单switch语句. 1-4产生计算和输出,而#5退出程序.我做了一个do / while循环,所以如果输入选项5,程序将结束.我收到一个错误: 4_19.c: In function ‘main’:4_19.c:95: error: ‘choice’ undeclared (first use in this function
尝试编译一个包含5个选项的简单switch语句. 1-4产生计算和输出,而#5退出程序.我做了一个do / while循环,所以如果输入选项5,程序将结束.我收到一个错误:
4_19.c: In function ‘main’: 4_19.c:95: error: ‘choice’ undeclared (first use in this function) 4_19.c:95: error: (Each undeclared identifier is reported only once 4_19.c:95: error: for each function it appears in.) 我不知道为什么它说它未宣布,因为我在开始时宣布它.我做错了什么?感谢名单.这是我的代码: /* C++ book. 4_19 The speed of sound in gases. Create a menu to choose between 4 gases. User then enters number of seconds it took to travel to destination. The program will calculate how far the source was (from speed that is unique to gas density). Validate input of seconds from 0 to 30 seconds only. */ #include <stdio.h> int main(void) { do { // Declare variables int choice; float speed,seconds = 0,distance; //Display program details and menu choice printf("n"); printf("Choose a gas that you would like to analyze.n"); printf("Medium Speed(m/s)n"); printf("1.Carbon Dioxide 258.0n"); printf("2.Air 331.5n"); printf("3.Helium 972.0n"); printf("4.Hydrogen 1270.0n"); printf("5.Quit Program"); printf("Enter a choice 1-5: "); scanf("%i",&choice); while (choice < 1 || choice > 5) // Validate choice input. { printf("You entered an invalid number. Choose 1,2,3,or 4 only.n"); printf("Enter a choice 1-5: "); scanf("%i",&choice); } // Switch statements to execute different choices switch(choice) { case 1: // Carbon Dioxide printf("Enter number of seconds,from 0 to 30,that the sound traveled in carbon dioxide: "); scanf("%f",&seconds); while (seconds < 0 || seconds > 30) // Validate time entered { printf("The range of input for seconds is only from 0 to 30 seconds.n"); printf("Please enter a valid number for number of seconds: "); scanf("%f",&seconds); } speed = 258.0; distance = speed * seconds; printf("The distance from the source of the sound is %.2f meters in carbon dioxide.n",distance); break; case 2: // Air printf("Enter number of seconds,that the sound traveled in air: "); scanf("%f",&seconds); } speed = 331.5; distance = speed * seconds; printf("The distance from the source of the sound is %.2f meters in air.n",distance); break; case 3: // Helium printf("Enter number of seconds,that the sound traveled in helium: "); scanf("%f",&seconds); } speed = 972.0; distance = speed * seconds; printf("The distance from the source of the sound is %.2f meters in helium.n",distance); break; case 4: // Hydrogen printf("Enter number of seconds,that the sound traveled in hydrogen: "); scanf("%f",&seconds); } speed = 1270.0; distance = speed * seconds; printf("The distance from the source of the sound is %.2f meters in hydrogen.n",distance); break; case 5: printf("End of Programn"); break; } } while (choice != 5); return 0; } 解决方法
你已经在do {} while循环中声明了选择;这意味着它只能在这两个括号内访问.但是,在你的while(choice!= 5)条件下,你会在括号之外再次引用它;这是一个错误.解决方案是将选项向上移动一级,并在main范围内声明它.
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