[Dev-C++] <Dec-C++>Please give me your feedbacks!

[Justin F. <jus...@gm...>]

Hi, 

I'm newer to C++ programming so I hope you can help me to improve my
coding skill. Here is my first code to implement Strtoi(char*), please
give me your feedback.
My lead ask me to implement it as Strtoi(wchar*), but I can't find
which head contains the definition of wchar and how to use it. And
some known bugs are there after tesing:

when I input a long string such as "12345678987654321", this app will crash.
Also when I add a sentence before sleep(), it crashed.

BTW, I want to know how to debug an app and how to track views I added.

Any ideas?

Thanks in advance and any suggestions will be appreciated!!

#include <stdlib.h>

int strtoi(char* a)
{
  
	int sum=0,size=0,i=0;

	while(a[i]!='\0') 		// calculate the size of the array
	{i++;size++;}
	
	printf("The size of string is: %d\n",size);
	i=0;
	
 
   	for(i=0;i<size;i++)	
	{
     if (a[i]<'0' || a[i]>'9') 		//Don't deal with invalid strings
       {	printf( "I think it's meaningless to covert a English word to
int.\n	Please input some string such as 123");
	        return 0;
       }
	else                       
	   {
	    int j=0;                    //variable 'j' refers to the exponet of 10
        int temp=a[i]-'0';              //covert a[i] to a interger
          for(j=size-i-1;j>0;j--)       //sum
             temp=temp*10; 
              
        sum+=temp;
        }
    }        
     printf("The result of convertion:%d\n",sum);
     return sum;
	
}	
int main()
{
  int i=0;
  char* a;
  printf("Please input your string,such as 123\n");
  scanf("%s",a);
  strtoi(a);	
  sleep(100000);
  return 0;
}

-- 
Thanks
Z.J.