Solve error: lvalue required as left operand of assignment
In this tutorial you will know about one of the most occurred error in C and C++ programming, i.e. lvalue required as left operand of assignment.
lvalue means left side value. Particularly it is left side value of an assignment operator.
rvalue means right side value. Particularly it is right side value or expression of an assignment operator.
In above example a is lvalue and b + 5 is rvalue.
In C language lvalue appears mainly at four cases as mentioned below:
- Left of assignment operator.
- Left of member access (dot) operator (for structure and unions).
- Right of address-of operator (except for register and bit field lvalue).
- As operand to pre/post increment or decrement for integer lvalues including Boolean and enums.
Now let see some cases where this error occur with code.
When you will try to run above code, you will get following error.
Solution: In if condition change assignment operator to comparison operator, as shown below.
Above code will show the error: lvalue required as left operand of assignment operator.
Here problem occurred due to wrong handling of short hand operator (*=) in findFact() function.
Solution : Just by changing the line ans*i=ans to ans*=i we can avoid that error. Here short hand operator expands like this, ans=ans*i. Here left side some variable is there to store result. But in our program ans*i is at left hand side. It’s an expression which produces some result. While using assignment operator we can’t use an expression as lvalue.
The correct code is shown below.
Above code will show the same lvalue required error.
Reason and Solution: Ternary operator produces some result, it never assign values inside operation. It is same as a function which has return type. So there should be something to be assigned but unlike inside operator.
The correct code is given below.
Some Precautions To Avoid This Error
There are no particular precautions for this. Just look into your code where problem occurred, like some above cases and modify the code according to that.
Mostly 90% of this error occurs when we do mistake in comparison and assignment operations. When using pointers also we should careful about this error. And there are some rare reasons like short hand operators and ternary operators like above mentioned. We can easily rectify this error by finding the line number in compiler, where it shows error: lvalue required as left operand of assignment.
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hi sir , i am andalib can you plz send compiler of c++.
i want the solution by char data type for this error
#include #include #include using namespace std; #define pi 3.14 int main() { float a; float r=4.5,h=1.5; {
a=2*pi*r*h=1.5 + 2*pi*pow(r,2); } cout<<" area="<<a<<endl; return 0; } what's the problem over here
#include using namespace std; #define pi 3.14 int main() { float a,p; float r=4.5,h=1.5; p=2*pi*r*h; a=1.5 + 2*pi*pow(r,2);
cout<<" area="<<a<<endl; cout<<" perimeter="<<p<<endl; return 0; }
You can't assign two values at a single place. Instead solve them differetly
Hi. I am trying to get a double as a string as efficiently as possible. I get that error for the final line on this code. double x = 145.6; int size = sizeof(x); char str[size]; &str = &x; Is there a possible way of getting the string pointing at the same part of the RAM as the double?
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How To Fix “error: lvalue required as left operand of assignment”
The message “error: lvalue required as left operand of assignment” can be shown quite frequently when you write your C/C++ programs. Check out the explanation below to understand why it happens.
Table of Contents
l-values And r-values
In C and C++, we can put expressions into many categories , including l-values and r-values
The history of these concepts can be traced back to Combined Programming Language. Their names are derived from the sides where they are typically located on an assignment statement.
Recent standards like C++17 actually define several categories like xvalue or prvalue. But the definitions of l-values and r-values are basically the same in all C and C++ standards.
In simple terms, l-values are memory addresses that C/C++ programs can access programmatically. Common examples include constants, variable names, class members, unions, bit-fields, and array elements.
In an assignment statement, the operand on the left-hand side should be a modifiable l-value because the operator will evaluate the right operand and assign its result to the left operand.
This example illustrates the common correct usage of l-values and r-values:
In the ‘x = 4’ statement, x is an l-value while the literal 4 is not. The increment operator also requires an l-value because it needs to read the operand value and modify it accordingly.
Similarly, dereferenced pointers like *p are also l-values. Notice that an l-value (like x) can be on the right side of the assignment statement as well.
Causes And Solutions For “error: lvalue required as left operand of assignment”
C/C++ compilers generates this error when you don’t provide a valid l-value to the left-hand side operand of an assignment statement. There are many cases you can make this mistake.
This code can’t be compiled successfully:
As we have mentioned, the number literal 4 isn’t an l-value, which is required for the left operand. You will need to write the assignment statement the other way around:
In the same manner, this program won’t compile either:
In C/C++, the ‘x + 1’ expression doesn’t evaluate to a l-value. You can fix it by switching the sides of the operands:
This is another scenario the compiler will complain about the left operand:
(-x) doesn’t evaluate to a l-value in C/C++, while ‘x’ does. You will need to change both operands to make the statement correct:
Many people also use an assignment operator when they need a comparison operator instead:
This leads to a compilation error:
The if statement above needs to check the output of a comparison statement:
if (strcmp (str1,str2) == 0)
C/C++ compilers will give you the message “ error: lvalue required as left operand of assignment ” when there is an assignment statement in which the left operand isn’t a modifiable l-value. This is usually the result of syntax misuse. Correct it, and the error should disappear.
Maybe you are interested :
- Expression preceding parentheses of apparent call must have (pointer-to-) function type
- ERROR: conditional jump or move depends on the uninitialized value(s)
- Print a vector in C++
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- error: lvalue required as left operand o
error: lvalue required as left operand of assignment
error lvalue required as left operand of assignment
here's my code:
#define doorSwitch 2 #define relay 4
void setup() { pinMode (doorSwitch, INPUT); pinMode (relay, OUTPUT); digitalWrite (relay, LOW); Serial.begin (9600); }
void loop() {
if(doorSwitch = HIGH) { digitalWrite(relay, HIGH ); delay(5000); digitalWrite(relay, LOW); } delay(1000); }
I'm just trying to make a relay turn on when I press a button
if(doorSwitch = HIGH) { you can't assign the value 1 (HIGH) to 2 (doorSwitch).
This is not a bootloader issue.
I'm guessing you are missing one of these =, and one of these digitalRead.
Please remember to use code tags when posting code
You have used doorSwitch as a symbolic constant. (Common C style would make it all upper-case letters: DOORSWITCH). Once the compiler's preprocessor pass is finished, your expression:
if(doorSwitch = HIGH)
actually looks like:
if(2 = HIGH)
to the compiler. Because you used the assignment operator (=) instead of the compare operator (==), the compiler wants a memory address (i.e., an lvalue) where to place the value for HIGH. Since "2" is not a variable, there's no memory address available for storing the value, hence the error.
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About the error: lvalue required as left operand of assignment. lvalue means an assignable value (variable), and in assignment the left value to the = has to be lvalue (pretty clear). Both function results and constants are not assignable ( rvalue s), so they are rvalue s. so the order doesn't matter and if you forget to use == you will get ...
lvalue means left side value.Particularly it is left side value of an assignment operator.
6. Put simply, an lvalue is something that can appear on the left-hand side of an assignment, typically a variable or array element. So if you define int *p, then p is an lvalue. p+1, which is a valid expression, is not an lvalue. If you're trying to add 1 to p, the correct syntax is:
Output: example1.cpp: In function 'int main()': example1.cpp:6:4: error: lvalue required as left operand of assignment. 6 | 4 = x; | ^. As we have mentioned, the number literal 4 isn't an l-value, which is required for the left operand. You will need to write the assignment statement the other way around: #include <iostream> using ...
"lvalue required as left operand of assignment" simply means that the left side of your assignment isn't an assignable address or convertible to one. PA0 is #defined as a simple constant without l-value properties.
error: lvalue required as left operand of assignment. johnmerlino. I get the following error: ... pointers_array.c:42:37: error: lvalue required as left operand of assignment ... #include <stdio.h> #include <string.h> #define MAXLINES 5000 /* max #lines to be sorted */ #define MAXLEN 1000 /* max length of any input line */ #define ALLOCSIZE ...
lvalue required as left operand of assignment. Hi all, it's been a long time since I did coding in C, but thought to pick up a very old project again, just to show off what I have been working on ten years ago. ... #include <stdlib.h> #include <stdio.h> #define bit1 1 #define bit2 2 #define bit3 4 #define bit4 8 #define bit5 16 #define bit6 32 ...
Check all your 'if' statements for equality. You are incorrectly using the assignment operator '=' instead of the equality operator '=='.
the only problem now is that if I use something like this final_price = price / total the output is always 0 so I tried show the output for the price itself by using `printf("%d", price); and it shows the value correctly. I don't know what is wrong exactly - Ali
= is an assignment operator. == is a comparison operator. This code is trying to assign the value 1 to Serial.read(), which it can't do. system March 26, 2010, 5:27pm
pinMode(trigePin = OUTPUT); pinMode(echooPin = INPUT); Look up the syntax for the pinMode function in the language reference. Read the how to use this forum-please read stickies to see how to properly post code.
3. The symbol pointer is an lvalue and can be used in an assignment on the left hand side. (++pointer), however, is not an lvalue and cannot be used in the same assignment. If on an alien planet far far away it did compile, this code would increment pointer by one and then set it to zero ( NULL) so to achieve the same effect, and be portable to ...
Hello everyone. I am working on a ssd1306 alien-blast style game and this is my code. I dont know why but everytime I try to check it, it says" lvalue required as left operand of assignment" Can somebody fix this please? #include <SPI.h> #include <Adafruit_GFX.h> #include <Adafruit_SSD1306.h> int a1h = 0; int a2h = 0; int a3h = 0; #define SCREEN_HEIGHT 64 #define SCREEN_WIDTH 128 #define OLED ...
4. The assignment operator = works by assigning whatever is on the right of the operator to the object on the left. So you are attempting to assign the value of sum, which is uninitialized, to the value resulting from x + y, which you cannot assign to. Looks like you really want to do: sum = x + y; It's not like in maths where the = operator ...
The name lvalue comes originally from the assignment expression E1 = E2, in which the left operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an object "locator value". What is sometimes called rvalue is in this International Standard described as the "value of an expression".
here's my code: #define doorSwitch 2 #define relay 4. void setup() {pinMode (doorSwitch, INPUT); pinMode (relay, OUTPUT); digitalWrite (relay, LOW); Serial.begin ...
You are trying to assign to a result from an operation another result. Try the following right way to do it: newArr = (newArr << i) ^ 1; The idea is that you have to have a valid lvvalue and the temporary result of the "<<" is not a valid one. You need a variable like newArr.
2. It means that you cannot assign to the result of an rvalue-expression, in this case the temporary returned by operator()(int,int). You probably want to change your non-const operator()(int,int) in the Matrix class to be: double& operator()( int x, int y ) { return A[i][j]; } Additionally (and unrelated to the question) you might want to ...
The problem here is you are trying to assign to a temporary / rvalue. Assignment in C requires an lvalue. I'm guessing the signature of your buttonPushed function is essentially the following. int buttonPushed(int pin);
0. In C, to provide a value for a function to return, you use a return statement: float lift_a_car(const int stick_length, const int human_weight, const int car_weight) {. return (double) stick_length * human_weight / (human_weight+car_weight); } In this code, I also inserted (double). In your original code, the expression is computed using ...
Assignment operators require that the left-hand side is an lvalue. This is where this jargon originates from. Postfix and prefix increment/decrement operators also have this requirement for their single operand. An lvalue expression may not be just a variable name, but also a more complex expression, for example: *(p + 2); // the unary ...