如果用float或者double計算精度不準(zhǔn)確的話，可用NSDecimalNumber進(jìn)行加減乘除

NSDecimalNumber* n1 = [NSDecimalNumber       decimalNumberWithString:[NSString    stringWithFormat:@"%f",d1]];

    NSDecimalNumber* n2 = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%f",d2]];

    NSDecimalNumber* n3 = [n1 decimalNumberByMultiplyingBy:n2];