arcsin and arccos in c++

#include <cmath>
...
radians = std::acos(number);

#include <iostream>
#include <stdlib.h>
#include <math.h>
#define PI 3.1415926535897932384626433832795

int main(int argc, char *argv[])
{
  while(1)
  {
    int input=0;
    double number=0.0f;
    double answer=0.0f;
    cout<<"What would you like to calculate?\n"
    "1. sine\n"
    "2. cosine\n"
    "3. tangent\n"
    "4. arcsine\n"
    "5. arccosine\n"
    "6. arctangent\n"
    "7. square root\n"
    "8. exit\n";
    cin>>input;
    if(input==8)
        break;
    cout<<"What number do you want to perform the operation on? ";
    cin>>number;
    bool radians=0;
    if(input>0&&input<4)
    {
        cout<<"In radians (0-no,1-yes):";
        cin>>radians;
    }
    if(!radians)
        number*=(PI/180);
    switch(input)
    {
        case 1:
            answer=sin(number);
        break;
        case 2:
            answer=cos(number);
        break;
        case 3:
            answer=tan(number);
        break;
        case 4:
            answer=asin(number)*(PI/180);
        break;
        case 5:
            answer=acos(number)*(PI/180);
        break;
        case 6:
            answer=atan(number)*(PI/180);
        break;
        case 7:
            answer=sqrt(number);
        break;
        default:
            system("cls");
            continue;
    }
    cout<<"Answer: "<<answer<<endl;
    cin.get();
    cin.get();
    system("cls");
  }
  cin.get();
  return 0;
}

    bool radians=0;
    if(input>0&&input<4)
    {
        cout<<"In radians (0-no,1-yes):";
        cin>>radians;
    }
    if(!radians)
        number*=(PI/180); 

if(!radians)
   number*=(PI/180);
 

if(!radians&&input>0&&input<4)
   number*=(PI/180);