错误必须是一个可修改的左值

Question

我试图做一个简单的货币转换器使用C，但由于某种原因它不断给我的错误“错误必须是一个可修改的左值”。 我检查了我的代码，并没有发现任何问题。任何帮助？

#include <stdio.h> 
#include <stdlib.h> 
    void main(){ 
     float jod_usd=1.41, usd_jod=0.71, jod_eur=1.26, eur_jod=0.8, currency; 
     char ic; 
     int f; 
     printf("Enter the number of your conversion option to continue...\n1- Convert from JOD\n2- Convert to JOD\n"); 
     scanf("%d",&f); 
     printf("Enter the character of your second currency to continue...\nU - - USD\nE - - EUR\n"); 
     scanf("%c",&ic); 
     printf("Enter your amount:\n"); 
     scanf("%f",&currency); 
     if(f==1&&(ic='U'||ic='u')){ 
      printf("%.2f JOD - - %.2f USD\n",currency,(currency*jod_usd)); 
     } 
     if(f==1&&(ic='E'||ic='e')){ 
      printf("%.2f JOD - - %.2f EUR\n",currency,(currency*jod_eur)); 
     } 
     if(f==0&&(ic='E'||ic='e')){ 
      printf("%.2f EUR - - %.2f JOD\n",currency,(currency*eur_jod)); 
     } 
     if(f==0&&(ic='U'||ic='u')){ 
      printf("%.2f USD - - %.2f JOD\n",currency,(currency*usd_jod)); 
     } 
     system("pause"); 

    } 

Answer 1

TL; DR使用=代替==的失误而导致此。

首先，您无意中更改了ic的值。

其次，由于操作者的优先级，

(ic='U'||ic='u') 

相同

((ic='U'||ic) = 'u') 

其中，的(ic='U'||ic)结果为不左值。

Answer 2

你确定它不只是一个简单的错误？你通常不会在条件中分配。如果我解决这个问题，那么你得到一些程序流程：

Enter the number of your conversion option to continue... 
1- Convert from JOD 
2- Convert to JOD 
1 
Enter the character of your second currency to continue... 
U - - USD 
E - - EUR 
Enter your amount: 

代码

#include <stdio.h> 
#include <stdlib.h> 
void main(){ 
    float jod_usd=1.41, usd_jod=0.71, jod_eur=1.26, eur_jod=0.8, currency; 
    char ic; 
    int f; 
    printf("Enter the number of your conversion option to continue...\n1- Convert from JOD\n2- Convert to JOD\n"); 
    scanf("%d",&f); 
    printf("Enter the character of your second currency to continue...\nU - - USD\nE - - EUR\n"); 
    scanf("%c",&ic); 
    printf("Enter your amount:\n"); 
    scanf("%f",&currency); 
    if(f==1 && (ic=='U' || ic=='u')){ 
     printf("%.2f JOD - - %.2f USD\n",currency,(currency*jod_usd)); 
    } 
    if(f==1&&(ic=='E'||ic=='e')){ 
     printf("%.2f JOD - - %.2f EUR\n",currency,(currency*jod_eur)); 
    } 
    if(f==0&&(ic=='E'||ic=='e')){ 
     printf("%.2f EUR - - %.2f JOD\n",currency,(currency*eur_jod)); 
    } 
    if(f==0&&(ic=='U'||ic=='u')){ 
     printf("%.2f USD - - %.2f JOD\n",currency,(currency*usd_jod)); 
    } 
    system("pause"); 

}