What I'm trying to do:
I need to write integers into a 2d array. The length of the array is N*N. So I scanf to get the value of N from the user.

The C/C extension gives the "expression must have a constant value". But building it with gcc works perfectly fine

What I've tried:
C/C extension gives error on N in both arrays, "expression must have a constant value".

After some googling answers, I tried to set my compiler version in the extension to c99, since that is the version which supports variable length arrays. But it still give the same error. Tried using other newer c versions, the intellicense still gives the same error.

Code and settings:
tree.c:

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

int main() {
    int N, i, j;
    scanf("%d", &N);
    int min_tree[N][N];
    int tree_walked[N];
}

c_cpp_properties.json:

{
    "name": "TUF_Laptop",
    "includePath": [
        "${workspaceFolder}/**",
        "/usr/local/include",
        "/usr/include",
        "/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/include",
        "/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/include-fixed",
        "/usr/lib/gcc/x86_64-pc-linux-gnu"
    ],
    "defines": [
        "_DEBUG",
        "UNICODE",
        "_UNICODE"
    ],
    "compilerPath": "/usr/bin/gcc",
    "intelliSenseMode": "linux-gcc-x64",
    "compilerArgs": [
        "-O3 -Wall -Wextra -std=c99"
    ],
    "cStandard": "c99",
    "cppStandard": "gnu  17",
    "compileCommands": ""
}

Similar answers I found: "expression must have a constant value" error in VS code for C

CodePudding user response：

The IDE may be warning you of a potential programming error, since value N can be changed while mintree and treewalked are still in scope. You should be able to fix this with the following modification:

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

int main() {
    int N_scan, i, j;
    scanf("%d", &N_scan);
    const int N = N_scan;
    int min_tree[N][N];
    int tree_walked[N];
}

The value of N cannot be changed while min_tree and tree_walked are in scope.

There is a similar answer (for a C case) here:

https://stackoverflow.com/questions/9219712/c-array-expression-must-have-a-constant-value#:~:text=expression must have a constant value. When creating,declared const: doesn't even provide a variable name.