ภาษาc++ผมผิดตรงไหนหรอครับช่วยดูให้หน่อยครับ มันไม่รัน

#include <studio.h>
void main ()
{
    char next ;
    int amount,deposit,inst;
    float interest;
    do {
        printf("enter car price:");scanf("%d",&amount);
        printf("enter deposit:");scanf("%d",&deposit);
        printf("enter inst:");scanf("%d",&inst);
        total=amount-deposit;
        inst=total+inst+months;
        total/months=(total+inst)/months;
        12 months=0.03;
        24 months=0.0325;
        48 months=0.035;
        60 months=0.04;
        72 months=0.0425;
        if(interest=12 months){
            interest= 0.03;
        }
         if(interest=24 months){
            interest= 0.0325;
        }
        if(interest= 48 months){
            interest= 0.035;
        }
         if(interest=60 months){
            interest= 0.04;
        }
        if(interest= 72 months){
            interest= 0.0425;
        }
    }}