循环控制语句for while do-while if switch

1：For 语句循环控制

L3执行完后直接执行L2的代码

int main()
{
 int a=0;
 for(int i=0;i<100;i=i+2)
{ a=a+10;
}
}

/************************/
.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$0, -4(%rbp) //a address
movl$0, -8(%rbp) //i address
jmp.L2
.L3:
addl$10, -4(%rbp) //a=a+10
addl$2, -8(%rbp)  //i=i+2
.L2:
cmpl$99, -8(%rbp) //i-99
jle.L3
movl$0, %eax
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits

2：while 语句

 

int main()
{
 int a=0;
 while(a<2)
{
  a++;
}

}


//**************************

.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$0, -4(%rbp)  //a=0
jmp.L2
.L3:
addl$1, -4(%rbp) //a++
.L2:
cmpl$1, -4(%rbp) //a-1
jle.L3
movl$0, %eax
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits

3: Do-while

 先执行后判断

int main()
{
 int a=20;
 do
{
  a++;
}while(a>100);

}



//**********************

.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$20, -4(%rbp)   //a=20
.L2:
addl$1, -4(%rbp) //a++
cmpl$100, -4(%rbp)   // a-100
jg.L2          大于 jg跳转
movl$0, %eax
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits

4：IF语句

  

int main()
{
 int a;
a=20;
if(a<30)
{a=66;
}
else if(a==30)
{a=99;
}else
{
 a=89;
}

}

//**********************

.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$20, -4(%rbp)  //a=20
cmpl$29, -4(%rbp)  //a-29
jg.L2            //a-29>0  跳L2
movl$66, -4(%rbp)  //a<=29 a=66
jmp.L3
.L2:
cmpl$30, -4(%rbp)  //a-30 
jne.L4            ZF标志位为0时跳转 zf=1时a==30
movl$99, -4(%rbp)  
jmp.L3
.L4:
movl$89, -4(%rbp)  //a=89;
.L3:
movl$0, %eax  //return 0
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits

5:swith

int main()
{
 int a;
a=20;
int b;
switch(a)
{
case 100:
 b=100;
 break;
case 20:
 b=20;
break;
default : b=0;
}
}
//*********************
.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$20, -4(%rbp)    //a=20
movl-4(%rbp), %eax   //eax=20
cmpl$20, %eax        //20-20
je.L3             //相等jmp .L3
cmpl$100, %eax      //20-100
jne.L7             // 不等 jmp .L7
movl$100, -8(%rbp)  //相等 b=100
jmp.L5
.L3:
movl$20, -8(%rbp)  //b=20
jmp.L5            //跳出
.L7:
movl$0, -8(%rbp)  //b=0
.L5:
movl$0, %eax
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits

6:continue break

continue 结束当下，继续下一个循环break 结束循环

int main()
{
 int a;
a=20;
int b;
for(int i=0;i<100;i++)
{
if(a==50)
{
b=50;
continue;
}
if(a==60)
{
b=60;
break;
}
a++;
}
}
//**************************
.file"b01.cpp"
.text
.globlmain
.typemain, @function
main:
.LFB0:
.cfi_startproc
pushq%rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq%rsp, %rbp
.cfi_def_cfa_register 6
movl$20, -4(%rbp) //a=20
movl$0, -8(%rbp)  //i=0;
jmp.L2
.L7:
cmpl$50, -4(%rbp) //a-50
jne.L3           //a!=50 jmp .L3
movl$50, -12(%rbp) //if a==50 b=50
jmp.L4            //continue
.L3:
cmpl$60, -4(%rbp)
jne.L5
movl$60, -12(%rbp)
jmp.L6             //break
.L5:
addl$1, -4(%rbp)    //a++
.L4:
addl$1, -8(%rbp) //i++
.L2:
cmpl$99, -8(%rbp) //i-99
jle.L7    //i<=99 jmp .L7
.L6:
movl$0, %eax
popq%rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.sizemain, .-main
.ident"GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-11)"
.section.note.GNU-stack,"",@progbits