如果用於字符串比較的語句沒有正確執行

Question

我想寫一個簡單的程序來找出不同形狀的區域。該程序編譯得很好，但是當它運行時它不會給我正確的答案。我的意思是當它運行它時會問：

你想找什麼區域？

，當我鍵入

方

或其他任何東西，然後回車，它只是結束，它不執行任何其他代碼。

代碼如下。

#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

點1：

使用strcmp()的字符串比較，不==運營商。

點2：

不管怎麼說，爲了char yourchoice[40]="";陣列，使用yourchoice[40]超出限制繼而調用undefined behaviour的。從0

點3 C開始數組索引：

printf()並不需要有一個指針的數據的參數。改變

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 

點4：

scanf()需要一個指針數據類型參數.Change

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

到

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

點5：^{與感謝先生@ Mints97}

您需要使用" "表示一個字符串字面。 ' ' 用於表示char。這兩個是不同的。

一般建議：

1. 推薦的原型main()是int main(void)
2. 總是初始化所有的局部變量。

Answer 2

你的代碼有很多錯誤。比較字符串使用strcmp而不是==

您

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

應該

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

Answer 3

你不能==比較C字符串。你需要strcmp()。而''用於單個字符，而不是字符串。

所以，改變

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>爲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); 

當您在標識符之前加上&時，它會返回該標識符的地址。你不需要在printf()

Answer 4

使用&當您使用

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

yourchoice[40]只有你是一個字符串比較單個字符。
即使這是錯誤的，因爲您聲明char yourchoice[40]意味着索引將從0到39。 使用strcmp函數來比較字符串。
如果字符串相同，則將返回0，否則返回1或-1。
使用

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

或者

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

---

而在你printf聲明不使用&打印變量的值。

改變這些線

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&這些行

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; 
    }