C关于函数

Question

我是编程新手，正在尝试编写一个具有 3 个函数的程序，要求用户输入 c 表示圆或 t 表示直角三角形。然后输入半径(如果是c)或两条边(如果是三角形)。我在使用 display 函数时遇到问题，它在两种情况下都将答案打印为 0 。如果我在圆形或三角形函数内输入 printf 语句，它会正确打印，但我需要函数 display。这是我的代码。任何见解将不胜感激。

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

#define M_PI 3.14

void circle(int num, double area, double per) {
    area = (double)(M_PI * pow(num, 2));
    per = (double)(2 * M_PI * num);
}

void rt(int num, int num1, double area, double per) {
    area = (double)(0.5 * num * num1);
    per = (double)((num + num1) + sqrt(pow(num, 2) + pow(num1, 2)));
}

void display(char entry, double area, double per) {
    if (entry == 'c') {
        printf("The circle has area %.1lf and perimeter %.1lf.\n", area, per);
    } else {
        printf("The right triangle has area %.1lf and perimeter %.1lf.\n", area, per);

    }
}

int main() {        
    char entry;
    int num;
    int num1;
    double area = 0;
    double per = 0;

    printf("Please enter 'c' for a circle or 't' for a right triangle\n");
    scanf("%c", &entry);
    if (entry == 'c') {
        printf("Please enter the radius for the circle.\n");
        scanf("%d", &num);
        getchar();
        circle(num, area, per);
    } else
    if (entry == 't') {
        printf("Please enter the length of two sides.\n");
        scanf("%d %d", &num, &num1);
        getchar();
        rt(num, num1, area, per);
    } else {            
        printf("Invalid input!");
    }

    display(entry, area, per);
    return 0;
}

Answer 1

您的circle和rt函数只是更新它们的参数，而不是main中的局部变量。您必须将指针传递给 circle 和 rt 来更新它们。

这是更正后的版本:

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

void circle(int num, double *area, double *per) {
    *area = M_PI * pow(num, 2);
    *per = 2 * M_PI * num;
}

void rt(int num, int num1, double *area, double *per) {
    *area = 0.5 * num * num1;
    *per = (num + num1) + sqrt(pow(num, 2) + pow(num1, 2));
}

void display(char entry, double area, double per) {
    if (entry == 'c') {
        printf("The circle has area %.1lf and perimeter %.1lf.\n", area, per);
    } else {
        printf("The right triangle has area %.1lf and perimeter %.1lf.\n", area, per);

    }
}

int main() {        
    char entry;
    int num, num1;
    double area = 0;
    double per = 0;

    printf("Please enter 'c' for a circle or 't' for a right triangle\n");
    scanf("%c", &entry);
    if (entry == 'c') {
        printf("Please enter the radius for the circle.\n");
        scanf("%d", &num);
        getchar();
        circle(num, &area, &per);
    } else
    if (entry == 't') {
        printf("Please enter the length of two sides.\n");
        scanf("%d %d", &num, &num1);
        getchar();
        rt(num, num1, &area, &per);
    } else {          
        printf("Invalid input!\n");
    }
    display(entry, area, per);
    return 0;
}