如果用于字符串比较的语句没有正确执行

Question

我想写一个简单的程序来找出不同形状的区域。该程序编译得很好，但是当它运行时它不会给我正确的答案。我的意思是当它运行它时会问：

你想找什么区域？

，当我键入

方

或其他任何东西，然后回车，它只是结束，它不执行任何其他代码。

代码如下。

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

int main() 
{ 
    char yourchoice[40]=""; 
    float a=0;; //a=height 
    float b=0; //b=breadth 
    float Sq,Rec,Parall,trap,cir,ell,tri; 

    printf("Here You can find out areas of Square,Rectangle,Parallelogram,trapezoid,circle,ellipse and triangle \n\n\n"); 

    printf("what do u want to find area of? : \n"); 
    scanf(" %s",yourchoice); 

    if(yourchoice[40]== 'square'){ 
     printf("Length of any side of the square ="); 
     scanf(" %f",&a); 
     Sq = pow(a,2); 
     printf("Area of the Square is %f",&Sq); 
    }else if(yourchoice== 'rectangle') 
    { 
     printf("Height = \n"); 
     scanf("%f",a); 
     printf("Width=\n"); 
     scanf("%f",b); 
     Rec= a*b; 
     printf("Area of the Rectangle : %f ",&Rec); 

    } 
    return 0; 
} 

Answer 1

点1：

使用strcmp()的字符串比较，不==运营商。

点2：

不管怎么说，为了char yourchoice[40]="";阵列，使用yourchoice[40]超出限制继而调用undefined behaviour的。从0

点3 C开始数组索引：

printf()并不需要有一个指针的数据的参数。改变

printf("Area of the Square is %f",&Sq); 
printf("Area of the Rectangle : %f ",&Rec); 

到

printf("Area of the Square is %f\n", Sq); //& not required 
printf("Area of the Rectangle : %f\n",Rec); //& not required 

点4：

scanf()需要一个指针数据类型参数.Change

scanf("%f",a); 
scanf("%f",b); 

到

scanf("%f", &a); // & is required 
scanf("%f", &b); // & is required 

点5：^{与感谢先生@ Mints97}

您需要使用" "表示一个字符串字面。 ' ' 用于表示char。这两个是不同的。

一般建议：

1. 推荐的原型main()是int main(void)
2. 总是初始化所有的局部变量。

Answer 2

你的代码有很多错误。比较字符串使用strcmp而不是==

您

if(yourchoice[40]== 'square')

应该

if(0 == strcmp(yourchoice, "square")) 

Answer 3

你不能==比较C字符串。你需要strcmp()。而''用于单个字符，而不是字符串。

所以，改变

if(yourchoice[40]== 'square') 

到

if(!strcmp(yourchoice, "square")) 

和

else if(yourchoice== 'rectangle') 

到

else if(!strcmp(yourchoice, "rectangle")) 

BTW，你需要包括<string.h>为strcmp()

另外，更改

printf("Area of the Square is %f",&Sq); 

到

printf("Area of the Square is %f", Sq); 
           ^
            no need of & 

和

printf("Area of the Rectangle : %f ",&Rec); 

到

printf("Area of the Rectangle : %f ",Rec); 

当您在标识符之前加上&时，它会返回该标识符的地址。你不需要在printf()

Answer 4

使用&当您使用

if(yourchoice[40]== 'square') 

yourchoice[40]只有你是一个字符串比较单个字符。
即使这是错误的，因为您声明char yourchoice[40]意味着索引将从0到39。 使用strcmp函数来比较字符串。
如果字符串相同，则将返回0，否则返回1或-1。
使用

if(strcmp(yourchoice, "square") == 0) 

或者

if(!strcmp(yourchoice, "square")) 

---

而在你printf声明不使用&打印变量的值。

改变这些线

printf("Area of the Square is %f",&Sq); 
printf("Area of the Rectangle : %f ",&Rec); 

到

printf("Area of the Square is %f",Sq); 
printf("Area of the Rectangle : %f ",Rec); 

---

而在你的其他部分，你忘了你的scanf

更改添加&这些行

scanf("%f",a); 
scanf("%f",b); 

要

scanf("%f",&a); // in scanf, '&' is required. 
scanf("%f",&b); 

Answer 5

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

    using namespace std; 

    int main() 
    { 
    char yourchoice[40]=""; 
    float a=0;; //a=height 
    float b=0; //b=breadth 
    float Sq,Rec,Parall,trap,cir,ell,tri; 

    printf("Here You can find out areas of Square,Rectangle,Parallelogram,trapezoid,circle,ellipse and triangle \n\n\n"); 

    printf("what do u want to find area of? : \n"); 
    scanf(" %s",yourchoice); 

//Here, strcmp is the prefered way to compare the strings 
//string.h is the header to use it 
// It returns 0 when the string match 
    //if(yourchoice == 'square'){ 
    if(!strcmp(yourchoice,"square")){ 
     printf("Length of any side of the square ="); 
     scanf(" %f",&a); 
     Sq = pow(a,2); 
//Second correction: & are to used only when storing the input and not while accessing or displaying it.So, in scanf you have to use but not for printf statements 

    printf("Area of the Square is %f",Sq); 
    } 
    else if(!strcmp(yourchoice,"rectangle")) 
    { 
     printf("Height = \n"); 
//Third Correction, in the org code you had missed to write "&" before the variable 'a' 
     scanf("%f",&a); 
     printf("Width=\n"); 
//Fourth Correction, in the org code you had missed to write "&" before the variable 'b' 
     scanf("%f",&b); 
     Rec= a*b; 
//Fifth correction: Same as second correction. Not to use '&' sign in printf statements 

     printf("Area of the Rectangle : %f ",Rec); 

    } 
    return 0; 
    }