foo.c: In function 'main':
foo.c:7:10: warning: implicit declaration of function 'c' [-Wimplicit-function-declaration]
     cout=c(n,m);
          ^
foo.c:8:10: warning: implicit declaration of function 'sum' [-Wimplicit-function-declaration]
     sout=sum(cout);
          ^~~
foo.c:9:14: error: 'scout' undeclared (first use in this function); did you mean 'sout'?
  printf("%d",scout);
              ^~~~~
              sout
foo.c:9:14: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:18: warning: variable 'sout' set but not used [-Wunused-but-set-variable]
     int n,m,cout,sout;
                  ^~~~
foo.c: In function 'sum':
foo.c:21:2: error: expected ',' or ';' before 'for'
  for(int i=0;i<k/2;i++)
  ^~~
foo.c:21:14: error: 'i' undeclared (first use in this function)
  for(int i=0;i<k/2;i++)
              ^
foo.c:21:23: error: expected ';' before ')' token
  for(int i=0;i<k/2;i++)
                       ^
foo.c:21:23: error: expected statement before ')' token
foo.c: In function 'main':
foo.c:6:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d",&m,&n);
     ^~~~~~~~~~~~~~~~~~~~

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