Implementation of c functions itoa and atoi

1. itoa function implementation

#include 
 
  void itoa(int i, char *string){        int power=0,j=0;        j=i;        for( power=1;j>10;j/=10)                power*=10;        for(;power>0;power/=10)        {                *string++='0'+i/power;                i%=power;        }        *string='\0';        printf("%s\n",string);}void main(){        char string[20];        itoa(12345, string);        printf("%s\n",string);}
 

Among them, power is equivalent to 1234, and its power is 1000; 134, and its power is 100.

* String ++ = '0' + I/power; // obtain the asicii code of the obtained character.

I/power get characters, such as 1234/1000 = 1; 234/100 = 2

2. atoi implementation

int atoi(char *str){        if(!str)                return -1;        bool bMinus=false;        int result=0;        if(('0'>*str || *str>'9')&&(*str=='+'||*str=='-'))        {               if(*str=='-')                bMinus=true;               *str++;        }        while( *str != '\0')        {                if('0'> *str || *str>'9')                        break;                else                        result = result*10+(*str++ - '0');        }        if (*str != '\0')//no-normal end                return -2;        return bMinus?-result:result;}

The overwritten atoi function does not consider overflow.

If ('0'> * str | * str> '9') & (* str = '+' | * str = '-')) // determine whether the first character is the plus or minus sign of a number

If (* str! = '\ 0') // no-normal end. When the preceding while LOOP does not exit normally, the string is deemed invalid, for example, "+ 1234abc"

Test:

char *c1 = "12345";        char *c2 = "-12345";        char *c3 = "bat-123";        char *c4 = "+123abc";        printf("c1=%d\n",atoi(c1));        printf("c2=%d\n",atoi(c2));        printf("c3=%d\n",atoi(c3));        printf("c4=%d\n",atoi(c4));

Output result:

C1 = 12345
C2 =-12345
C3 =-2
C4 =-2