Resolving the “error: assignment to expression with array type error” When Assigning a Struct Field in C

As a beginner in C programming, it’s common to face challenges when experimenting with new concepts. One such concept is working with structs. Let’s dive into a common error encountered by new programmers and discuss how to fix it.

Understanding the Problem

Here’s an example of a code snippet that triggers the “error: assignment to expression with array type error” when assigning a struct field:

#include <stdio.h>

#define N 30

typedef struct{
     char name[N];
     char surname[N];
     int age;
} data;

int main() {
     data s1;
     s1.name="Maria";
     s1.surname = "Lari";
     s1.age = 19;
     getchar();
     return 0;
}

When attempting to compile the code above, the compiler reports an error on the lines where s1.name and s1.surname are being assigned. However, if you use the following code, it works:

data s1 = {"Maria", "Lari", 19};

Reason Behind the Error

The error occurs because the left-hand side (LHS) of the assignment in question uses an array type, which is not assignable. In C programming, an assignment operator requires a modifiable lvalue as its left operand. A modifiable lvalue is an lvalue that does not have an array type.

Solution to the Problem

To fix the error, you need to use the strcpy() function to copy the string into the array:

strcpy(s1.name, "Maria");
strcpy(s1.surname, "Lari");

Now, the assignment should work correctly.

Using Initialization Instead of Assignment

It’s important to understand the difference between assignment and initialization. In the example that works, we are not using a direct assignment involving an assignment operator. Instead, we use a brace-enclosed initializer list to provide the initial values for the object, following the rules of initialization in C programming.

Key Takeaways

• Using an array type in a direct assignment causes the “error: assignment to expression with array type error.”
• To assign strings to struct fields with an array type, use the strcpy() function.
• Initializing a struct with a brace-enclosed initializer list is an alternative approach that avoids the error.

In conclusion, understanding the difference between assignment and initialization, as well as the limitations of array types in C programming, can help you avoid this common error. Keep practicing and experimenting with different code snippets to improve your understanding of C programming concepts and become a more proficient programmer.