C语言字符串比较编译错误：需使用显式字符串比较函数

核心问题解决：字符串比较错误 #

你遇到的编译错误是因为在C语言中，不能直接用==比较字符串内容。choice_1是字符数组的首地址，"1"是字符串字面量的内存地址，==比较的是这两个地址是否相同，而非字符串内容是否一致。

要正确比较字符串内容，需使用<string.h>头文件提供的strcmp函数：

• 当strcmp(str1, str2)返回0时，说明两个字符串内容完全相等
• 返回正数表示str1大于str2，负数表示str1小于str2

把你的判断代码修改为：

if (strcmp(choice_1, "1") == 0) {
    // 2D图形处理逻辑
} else if (strcmp(choice_1, "2") == 0) {
    // 3D图形处理逻辑（可后续补充）
} else {
    printf("无效输入，请输入1或2\n");
}

代码其他问题修复 #

除了字符串比较，你的代码还有几个会导致运行异常的问题：

1. Switch Case缺少break #

每个case执行完后没有break;，会导致程序继续执行后续所有case的代码（比如选了正方形后会接着执行矩形、三角形的逻辑）。在每个case的末尾添加break;：

case '1':{
    // 正方形逻辑
    break; // 退出switch
}

2. 字符输入读取残留换行符 #

scanf("%c",&_2dshape);会读取上一次scanf后留在输入缓冲区的换行符，导致直接跳过输入。修改为：

scanf(" %c",&_2dshape); // 前面加空格，自动跳过空白字符（换行、空格等）

3. 公式错误修正 #

• 三角形面积：应该是(底×高)/2，你代码里没除以2
• 菱形面积：对角线乘积的一半，修改为(diagonal1 * diagonal2) / 2
• 梯形面积：正确公式是(上底+下底)×高/2，你的代码写成了length*diagonal1*diagonal2，要改成(diagonal1 + diagonal2) * length / 2
• 风筝面积：应该是对角线乘积的一半，不是直接相乘

4. 冗余变量与输入格式问题 #

• _3dshape变量未使用，可以删除
• scanf("%f\n%f",&length,&breadth);里的\n多余，会导致输入异常，改成scanf("%f %f",&length,&breadth);

修改后的完整代码 #

#include<stdio.h>
#include <string.h>
#define PI 3.14159

int main()
{
    char name[100], choice_1[100], shape_choice;
    float length, breadth, SA, perimeter, diagonal1, diagonal2, height;

    printf("What should we call you?\n>>");
    scanf("%s", name);

    printf("Hello %s :)\nThis Program will help you calculate the SA, Volume, Perimeter and Circumference of your geometric shapes!\nInput your choice below:\n", name);
    printf("What Shapes are we looking at?\n(1)2 Dimensional (2)3 Dimensional\n>>");
    scanf("%s", choice_1);

    if (strcmp(choice_1, "1") == 0)
    {
        printf("Which Shape's Area and Perimeter do you want to find out?\n1.Square 2.Rectangle 3.Triangle 4.Rhombus 5.Parallelogram 6.Kite 7.Trapezoid\n>>");
        scanf(" %c", &shape_choice);

        switch(shape_choice){
            case '1':{
                printf("You chose square\nThe formula of perimeter of square is 4*side and that of area of square is side*side\nEnter the length of each side of square below:\n>>");
                scanf("%f", &length);
                perimeter = 4 * length;
                printf("The Perimeter of Square is: %.2f units\n", perimeter);
                SA = length * length;
                printf("The Area of Square is: %.2f square units\n", SA);
                break;
            }
            case '2':{
                printf("You chose Rectangle\nThe formula of perimeter of Rectangle is 2*(length+breadth) and that of area of Rectangle is length*breadth\nEnter the values of length and breadth below:\n>>");
                scanf("%f %f", &length, &breadth);
                perimeter = 2 * (length + breadth);
                printf("The Perimeter of Rectangle is: %.2f units\n", perimeter);
                SA = length * breadth;
                printf("The Area of Rectangle is: %.2f square units\n", SA);
                break;
            }
            case '3':{
                printf("You chose Triangle\nThe formula of perimeter of Triangle is sum of all three sides and that of area of Triangle is (base*height)/2\nEnter the values of three sides below:\n>>");
                float side2, side3;
                scanf("%f %f %f", &length, &side2, &side3);
                perimeter = length + side2 + side3;
                printf("The Perimeter of Triangle is: %.2f units\n", perimeter);
                printf("Enter the values of base and height below:\n>>");
                scanf("%f %f", &length, &height);
                SA = (length * height) / 2;
                printf("The Area of Triangle is: %.2f square units\n", SA);
                break;
            }
            case '4':{
                printf("You chose Rhombus\nThe formula of perimeter of Rhombus is 4*side and that of area of Rhombus is (product of diagonals)/2\nEnter the length of a side below:\n>>");
                scanf("%f", &length);
                perimeter = 4 * length;
                printf("The Perimeter of Rhombus is: %.2f units\n", perimeter);
                printf("Enter the values of the two diagonals below:\n>>");
                scanf("%f %f", &diagonal1, &diagonal2);
                SA = (diagonal1 * diagonal2) / 2;
                printf("The Area of Rhombus is: %.2f square units\n", SA);
                break;
            }
            case '5':{
                printf("You chose Parallelogram\nThe formula of perimeter of Parallelogram is 2*(side1+side2) and that of area of Parallelogram is base*height\nEnter the values of side 1 and side 2 below:\n>>");
                scanf("%f %f", &length, &breadth);
                perimeter = 2 * (length + breadth);
                printf("The Perimeter of Parallelogram is: %.2f units\n", perimeter);
                printf("Enter the values of base and height below:\n>>");
                scanf("%f %f", &length, &height);
                SA = length * height;
                printf("The Area of Parallelogram is: %.2f square units\n", SA);
                break;
            }
            case '6':{
                printf("You chose Kite\nThe formula of perimeter of Kite is 2*(side1+side2) and that of area of Kite is (product of diagonals)/2\nEnter the values of the two unequal sides below:\n>>");
                scanf("%f %f", &length, &breadth);
                perimeter = 2 * (length + breadth);
                printf("The Perimeter of Kite is: %.2f units\n", perimeter);
                printf("Enter the values of the two diagonals below:\n>>");
                scanf("%f %f", &diagonal1, &diagonal2);
                SA = (diagonal1 * diagonal2) / 2;
                printf("The Area of Kite is: %.2f square units\n", SA);
                break;
            }
            case '7':{
                printf("You chose Trapezoid\nThe formula of perimeter of Trapezoid is sum of all sides and that of area of Trapezoid is (sum of two parallel sides)*height/2\nEnter the values of all four sides below:\n>>");
                float side3, side4;
                scanf("%f %f %f %f", &length, &breadth, &side3, &side4);
                perimeter = length + breadth + side3 + side4;
                printf("The Perimeter of Trapezoid is: %.2f units\n", perimeter);
                printf("Enter the values of the two parallel sides and height below:\n>>");
                scanf("%f %f %f", &diagonal1, &diagonal2, &height);
                SA = (diagonal1 + diagonal2) * height / 2;
                printf("The Area of Trapezoid is: %.2f square units\n", SA);
                break;
            }
            default:{
                printf("无效的选择，请输入1-7之间的数字\n");
                break;
            }
        }
    } else if (strcmp(choice_1, "2") == 0) {
        printf("3D图形功能将在后续版本中添加\n");
    } else {
        printf("无效输入，请输入1或2\n");
    }

    return 0;
}

内容的提问来源于stack exchange，提问作者Daksh Shukla