CareerCup

#include<stdio.h>
#include<strings.h>

char exploreString(char str[],int k)
{
int i=0;
int current=0;
int l=strlen(str) ;
for(i=0;i<l;i++)
{
if(str[i]>47 &&str[i]<55)
{
current+=str[i]-'0' ;
if(k<=current)
return str[i-1] ;
}

}
printf("k is not in string\n") ;
}

void main()
{
char str[50],ch ;
int k;
printf("enter the string\n") ;
scanf("%s",str) ;
printf("enter the number\n") ;
scanf("%d",&k) ;
ch=exploreString(str,k) ;
printf("%c",ch) ;
}

all codes having time complexity O(n^2) anyone with efficient approach
...