// verify "type" can contain the values

char chars[] = {"753"}; // ASCII
byte charlen = sizeof(chars) / sizeof(chars[0]) - 1; // length of chars[] minus <CR>
long accumulator; // accumulator

void setup() {
  Serial.begin(115200);
  for (byte i = 0; i < charlen; i++) { // count through characters
    long digit = chars[i] - 48; // change ASCII to INT
    int power = charlen - i - 1; // local variable
    digit = digit * placevalue(power); // digit * 10 ^ place
    accumulator += digit; // add result of digit * 10 ^ place
  }
  Serial.print("result ");
  Serial.println(accumulator);
}

void loop() {}

long placevalue(int exponent) {
  long power = 1; // reset local power
  for (int i = 0; i < exponent; i++) { // count backwards 3, 2, 1
    power *= 10; // accumulate the exponents
  }
  return (power);
}