RE on line 9?

#include<bits/stdc++.h>
#define int long long
using namespace std;
struct mat{
    int n,m;
    int a[605][605];
    mat(){memset(a,0,sizeof(a));}
};
void f(){
    int n;cin>>n;
    mat a,b,c;
}
signed main(){
    f();
    return 0;
}

{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: g++ 生成活动文件",
            "command": "/usr/bin/g++",
            "args": [
                "-std=c++17",
                "-g",
                "${file}",

                "-I",
                "/home/fkxr/midifile/include",

                "/home/fkxr/midifile/lib/libmidifile.a",

                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "调试器生成的任务。"
        }
    ],
    "version": "2.0.0"
}