c - 如何解决错误: else without a previous if

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已关闭。这个问题是 not reproducible or was caused by typos 。目前不接受答案。

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这个问题是由拼写错误或无法再重现的问题引起的。虽然类似的问题可能是 on-topic在这里，这个问题的解决方式不太可能帮助 future 的读者。

已关闭 7 年前。

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我已经尝试解决这个错误半个小时了。我如何让这段代码工作？

输入完毕，请指出错误。

#include <stdio.h>
#include <math.h>

void main()
{
const float pi = 3.142;
int choice;
float radius, volume, volts, ohms, watts, mass, accel, force;

printf("\n1. Calculate the volume of a sphere");
printf("\n2. Calculate the power of a circuit");
printf("\n3. Calculate the force of an object");
printf("\n-----------------------------------\n");
printf("What is your choice? : ");
scanf("%d", &choice);

if(choice==1)
    printf("Enter value of radius (cm) : ");
    scanf("%f", &radius);
    volume = 4/3 * pi * pow(radius,3);
    printf("Volume of a sphere is %.2f", volume);
    else if(choice==2)
        printf("Enter value of voltage (volts) : ");
        scanf("%f", &volts);
        printf("Enter value of resistance (ohms) : ");
        scanf("%f", &ohms);
        watts = pow(volts,2) / ohms;
        printf("Power of circuit is : %.2f watts", watts);
        else if(choice==3)
            printf("Enter mass of object (kg)                : ");
            scanf("%f", &mass);
            printf("Enter acceleration (meters per second squared) : ");
            scanf("%f", &accel);
            force = mass * accel;
            printf("The force of the object is : %.2f Neutons", force);
            else
                printf("You've entered an invalid choice...");
getch();
}

Answer 1

如果 if/else block 有多行，请使用大括号:

if (choice==1) {
    printf("Enter value of radius (cm) : ");
    scanf("%f", &radius);
    volume = 4/3 * pi * pow(radius,3);
    printf("Volume of a sphere is %.2f", volume);
} else if (choice==2) {
    printf("Enter value of voltage (volts) : ");
    scanf("%f", &volts);
    printf("Enter value of resistance (ohms) : ");
    scanf("%f", &ohms);
    watts = pow(volts,2) / ohms;
    printf("Power of circuit is : %.2f watts", watts);
} else if (choice==3) {
    printf("Enter mass of object (kg)                : ");
    scanf("%f", &mass);
    printf("Enter acceleration (meters per second squared) : ");
    scanf("%f", &accel);
    force = mass * accel;
    printf("The force of the object is : %.2f Neutons", force);
} else printf("You've entered an invalid choice...");

如果没有大括号，您的代码将被解释为

// Standalone if block
if (choice==1) 
    printf("Enter value of radius (cm) : ");
// End of the if block
// ...
// else without previous if (syntax error)
else if (choice==2)
    printf("Enter value of voltage (volts) : ");