clear
//Given
u=4*3.14*10**-7                     //T/A m
n=20
I=12                                  //A
r=0.1                                 //m

//Calculation
B=u*n*I/(2*r)

//Result
printf("\n Magnetic field at the centre of coil is %0.1f  *10**-3 T",B*10**3)