Modify cpp.yml for build path and C++20 standard

Author: Sirivasv

.github/workflows/cpp.yml

@@ -5,10 +5,12 @@ on:
     branches: [ "main" ]
     paths:
       - 'cpp/**'
+      - '.github/workflows/cpp.yml'
   pull_request:
     branches: [ "main" ]
     paths:
       - 'cpp/**'
+      - '.github/workflows/cpp.yml'
 
 jobs:
   build:
@@ -25,6 +27,6 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - name: build
-      run: g++ -o a.out main.cpp
+      run: g++ -std=c++20 -o a.out main.cpp
     - name: run
       run: ./a.out < input.in