This is a little Python script for learning, nothing serieus, but working.

command = ""
def calc_volt():
    var_i = input(" Amp : ")
    var_r = input(" Ohm : ")
    var_v = round(float(var_i) * float(var_r), 2)
    print(str(var_i) + " * " + str(var_r) + " = " + str(var_v) + " volt" + '\n')

def calc_amp():
    var_v = input("Volt : ")
    var_r = input(" Ohm : ")
    var_i = round(float(var_v) / float(var_r), 2)
    print(str(var_v) + " / " + str(var_r) + " = " + str(var_i) + " amp" + '\n')

def calc_ohm():
    var_v = input("Volt : ")
    var_i = input(" Amp : ")
    var_r = round(float(var_v) / float(var_i), 2)
    print(str(var_v) + " / " + str(var_i) + " = " + str(var_r) + " Ohm" + '\n')

def calc_watt_iv():
    var_i = input(" Amp : ")
    var_v = input("Volt : ")
    var_p = round(float(var_i) * float(var_v), 2)
    print(str(var_i) + " * " + str(var_v) + " = " + str(var_p) + " Watt" + '\n')

def calc_watt_pv():
    var_p = input("Watt : ")
    var_v = input("Volt : ")
    var_i = round(float(var_p) / float(var_v), 2)
    print(str(var_p) + " / " + str(var_v) + " = " + str(var_i) + " Amp" + '\n')

while(command != 0):
    print("Choose what to calculate: ")
    print("1: Voltage")
    print("2: Ampère")
    print("3: Resistance")
    print("4: Watt from Volt & Amp DC/AC single phase")
    print("5: Amps from Watt & Volt DC/AC single phase")
    print("0: Exit")
    print("")
    command = int(input("Your choice: "))
    if(command == 1):
        calc_volt()
    elif(command == 2):
        calc_amp()
    elif(command == 3):
        calc_ohm()
    elif(command == 4):
        calc_watt_iv()
    elif(command == 5):
        calc_watt_pv()
    elif(command == 0):
        print("Good bye")
    else:
        print("Not a valid option" + '\n')