Question

Please briefly explain these C++ programmings below

ps. isNumber is a bool function name, it takes a char as input and returns a boolean value.

isNumber returns true if the character is a number from 0 to 9, otherwise it returns false.

| double retrieveNumber(string expression, int& idx) { double ans = 0; while (isNumber(expression[ idx])) { ans *= 10; ans += expression[ idx] - '0'; idx++; 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 if (expression[ idx] ='.') { double decimal = 0, digits = 1; idx++; while (isNumber( expression[ idx])) { digits *= 10; decimal *= 10; decimal += expression[ idx] - '0'; idx++; decimal /= digits; return ans + decimal; return ans;

Answer 1

The function will convert whatever the string we send into double value

Let's take one example

expression = "342.567"

and idx points to 0 th index

The first while loop has condition until it is a number it will loop when it comes to '.' it will exit

first it will take value 3

ans=0*10=0

ans=0+3=3 subtraction to character 0 here is used to convert charcter value of 3 to integer value

idx moves next position points to value 4

ans =3*10=30

ans=30+4=34

idx moves to 3rd value 2

ans=34*10=340; 340+2=342

Next index is '.' it stops loop here and checks condition if it is '.' it is so

from next point onwards we will calculate digits and decimal value digits is used to divide the value upto that many decimals to get in floating type

In the same way how calculated above we calculate 567 and store it in decimal

decimal=567 and digits=1000(as we have 3 digits)

we update decimal to 567/1000 which makes 0.567

at last we add it to the integer value we got previous result=342+0.567=342.567

It returns 342.567

for example if we have 342.w234 it will return 342.0

The function calculates upto we get the numeric character otherwisse it will stop and return upto there

If value=64h.764 returns 64.0

comment if any doubts