int fm(int a,int b) {if(b==1)return a; else return a+fm(a,b-1); } main( ) { printf("%d\n",fm(4,3))

int fm(int a,int b) {if(b==1)return a; else return a+fm(a,b-1); } main( ) { printf("%d\n",fm(4,3))
int fm(int a,int b) {if(b==1)return a; else return a+fm(a,b-1); } main( ) { printf("%d\n",fm(4,3))

int fm(int a,int b) {if(b==1)return a; else return a+fm(a,b-1); } main( ) { printf("%d\n",fm(4,3))
fm(4,3)
b=3≠1
return a+fm(a,b-1)=4+fm(4,2)
fm(4,2)
b=2≠1
return a+fm(a,b-1)=4+fm(4,1)
fm(4,1)
b=1
return a

∴fm(4,1)=4
f(4,2)=4+4=8
f(4,3)=4+8=12
最后输出12