Error: invalid lvalue in assignment [in c]

Question

CAN'T FIND WHAT'S WRONG...

I have been programming and trying to fix a problem here but I can't find a bug. Could you guys help me advice what did I code wrong in this program? It will be thankful :)

This is what complier said after I complied the program:

In function 'main':
Line 40: error: invalid lvalue in assignment

which is:

/*Calculate area for single room*/
width * length = totalArea_single;

And here's the whole code:

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

/*Main function of this program*/
int main()
{
char input[512];/*buffer*/
char roomInput[512];/*buffer*/
int roomCount =0;/*Store number of room*/
int width =0;/*width integer*/
int length =0;/*length integer*/
int room =0;/*To make sure roomCount have to be more than 0*/
int totalArea_single =0;
int totalArea_all =0;  

/*Ask how many room in the house*/
printf("\nHow many rooms in the house?: ");
fgets(input,sizeof(input),stdin);
sscanf(input,"%d",&roomCount);

/*For loop for calculating room area by number of room entered*/
for(room=0;room<roomCount;room++)
{
    /*Input for width and have to be more than 0*/
    while(width>0)
    {
        printf("Width in meters for room %d: ",room+1);
        fgets(roomInput,sizeof(roomInput),stdin);
        sscanf(roomInput,"%d",&width);
    }

    /*Input for length and have to be more than 0*/
    while(length>0)
    {
        printf("Length in meters for room %d: ",room+1);
        fgets(roomInput,sizeof(roomInput),stdin);
        sscanf(roomInput,"%d",&length);
    }

    /*Calculate area for single room*/
    width * length = totalArea_single;

    /*Store area of all rooms*/
    totalArea_all = totalArea_single + totalArea_all;

    width = -1;
    length = -1;
}

/*Print out total areas of the house*/
printf("\nTotal areas of the house is %d square meters",totalArea_all);

return 0;
}

I'm not sure what did I do wrong... Thanks for your help :)

Solution 1

If you have closer look to your compiler error you can see that, it say's

error: invalid lvalue in assignment

So to better understand this error you have to understand what is lvalue and rvalue. An lvalue refers to an object that persists beyond a single expression. You can think of an lvalue as an object that has a name. On the other side an rvalue is a temporary value that does not persist beyond the expression that uses it.

So if you look code line which causing this issue

width * length = totalArea_single;

So while storing any value/data you need to have lvalue on left hand side of = operator. While width * lenght generates a rvalue which can't store any value, in simple words you can say that to store any value you need lvalue. That's why you need to change this statement to

totalArea_single = width * length;

For more details about lvalue and rvalue please refer to this SO Link.

Solution 2

Should be

totalArea_single = width * length;

instead of

width * length = totalArea_single;