foo.c: In function 'main':
foo.c:6:13: error: 's1' undeclared (first use in this function)
    6 |  scanf("%s",s1);
      |             ^~
foo.c:6:13: note: each undeclared identifier is reported only once for each function it appears in
foo.c:8:2: error: 's2' undeclared (first use in this function)
    8 |  s2[0]=temp;
      |  ^~

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