CareerCup

int a2i(char* str)
{
   int num = 0;
   int i=0;
   
   for(i=0;i<strlen(str);i++)
   {
      num = num*10 + str[i] - '0';
   }
 
 return num;
}

<pre lang="c++" line="1" title="CodeMonkey52824" class="run-this">int num = 0;
int mul = 1;

for(int i=0; i < strlen(str); mul *= 10, ++i)
{
num += (str[i] - 0x30) * mul;
}

</pre><pre title="CodeMonkey52824" input="yes">
</pre>

in the for loop
{
num*=10;
num+= char[i] - '0';
}

#include<stdio.h>
#include<string.h>
int main()
{
char b[]="-40";
int flag=1;
int num=0;
for(unsigned int i=0;i<strlen(b);i++){
if(b[i]=='-') flag=-1;
else num=num*10+b[i]-'0';
}
printf("%d",flag*num);
}

int Ascii_To_Int (char * str)
{
int num = 0;
int mul = 1;
int End = strlen(str);

for(int i = End-1; i >= 0 ; mul *= 10, i--)
{
num += (str[i] - 0x30) * mul;
}

return num;
}

I didn't get the question correctly. can any one post a sample input and output value?

what do you mean by ASCII representation? Is it any different from string representation

what about int overflow?

int atoi(char *str, int strLen){
int sign = 1;
int i = 0;
int result = 0;

if(str == NULL) return -1;
if(str[i] == '-') {
sign = -1;
i++;
}

while (i < strLen){
if(isdigit(str[i])){
checkIntOverflow(result, INT_MAX);
result = result*10 + str[i] - '0';
}else{
fprintf(stderr, "not valid integer string\n");
}
i++;
}
return result;
}

enum err_t
{
	ERR_OK,
	ERR_ARG,
	ERR_INVAL,
	ERR_OVERFLOW,
};
typedef int BOOL;
#define TRUE 1
#define FALSE 0

err_t atoi(const char *str, int *num)
{
	BOOL negative = FALSE;
	err_t err = ERR_OK;
	unsigned int result = 0, temp;
	unsigned int addition;

	if (num == NULL) {
		err = ERR_ARG;
		goto out;
	}

	if (str == NULL) {
		err = ERR_ARG;
		goto out;
	}

	if (*str == '-') {
		negative = TRUE;
		++str;
	} else if (*str == '+') {
		++str;
	}

	while (*str) {
		if (*str >= '0' && *str <= '9') {
			addition = (unsigned int)(*str - '0');
			if (0 != (result & (0xF0 << (8 * (sizeof(unsigned int) - 1))))) {
				err = ERR_OVERFLOW;
				goto out;
			} 

			temp = result << 1; // temp = result * 2;
			result <<= 3;  // result *= 8;

			if (temp + result < result) {
				err = ERR_OVERFLOW;
				goto out;
			}
			result = temp + result;  // finally multiplied by 10, NO overflow.

			if (addition + result < result) {
				err = ERR_OVERFLOW;
				goto out;
			}
			result += addition;
			++str;
		} else {
			err = ERR_INVAL;
		}
	}

	if (0 != (result & (1 << (8 * sizeof(unsigned int) - 1)))) {
		err = ERR_OVERFLOW;
		goto out;
	}

	*num = (int)result;
	if (negative) {
		*num *= -1;
	}

out:
	return err;
}

int Atoi(const char * ptr) {
  long long rs = 0;
  bool minus = false;
  while (*ptr == ' ') ptr++;
  if (*ptr == '-') {
    minus = true;
    ptr++;
  } else if (*ptr == '+') ptr++;
  while (*ptr >= '0' && *ptr <= '9') {
    rs = rs * 10 + *ptr - '0';
    ptr++;
    if (rs > INT_MAX) break;
  }
  if (minus) rs *= -1;
  if (rs > INT_MAX) return INT_MAX;
  if (rs < INT_MIN) return INT_MIN;
  return rs; 
}

user atoi