foo.c:2:1: warning: return type defaults to 'int' [-Wimplicit-int]
    2 | Shan(int a[500][500],int m,int n)
      | ^~~~
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o: in function `_start':
(.text+0x24): undefined reference to `main'
collect2: error: ld returned 1 exit status

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