Main.c: In function 'main':
Main.c:9:7: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
    9 |    a1=abs(a),b1=abs(b);
      |       ^~~
Main.c:12:16: error: 'a2' undeclared (first use in this function); did you mean 'a1'?
   12 |     else if(a1>a2) s=a1+b1*2;
      |                ^~
      |                a1
Main.c:12:16: note: each undeclared identifier is reported only once for each function it appears in
Main.c:7:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    7 |     scanf ("%d %d",&a,&b);
      |     ^~~~~~~~~~~~~~~~~~~~~