how can I convert character to integer number

Question

How could I change an array of character (string) to an integer number without using any ready function (ex atoi();) for example :-

 char a[5]=\'4534\';
         


        

Answer 1

First of all this statement

 char a[5]='4534';

will not compile. I think you mean

 char a[5]="4534";
           ^^   ^^

To convert this string to a number is enough simple.

For example

int number = 0;

for ( const char *p = a; *p >= '0' && *p <= '9'; ++p )
{
    number = 10 * number + *p - '0';
}

Or you could skip leading white spaces.

For example

int number = 0;

const char *p = s;

while ( std::isspace( ( unsigned char )*p ) ) ++p;

for ( ; *p >= '0' && *p <= '9'; ++p )
{
    number = 10 * number + *p - '0';
}

If the string may contain sign '+' or '-' then you can check at first whether the first character is a sign.