Question

C++ LANGUAGE

Using only pointer notation, implement and test the following functions that operate on C Strings:

char *strStr(const char *s1, const char *s2)

- Locates the string s2 as a substring of s1 and returns a pointer to its first occurrence in s1 or nullptr if s2 is not a substring of s1

char *strrChr(constant char *s, int ch)

- Returns a pointer to the last occurrence of the character ch in string s or nullptr if ch is not in s

longAtoL(const char *s)

- Converts string s into an integer, stops after the first non digit is found: e.g. for string "123.45" number 123 is returned

Answer 1

```

#include<bits/stdc++.h>

using namespace std;

char* strStr( char* s1, char* s2){
    int j=0,i=0;
    bool flag = false;
  
    while(s1[i]!='\0'){
      
        if(s1[i]!=s2[j]){
            j=0;
        }
      
        i++;
        j++;
        if(s2[j] == '\0'){
            flag = true;
            break;
        }
    }
  
    if(flag){
        char* temp = &s1[i-j];
    }else{
        return NULL;
    }
}

char* strrchr(char* s,char ch){
    int i=0;
    char* ans = NULL;
    while(s[i]!='\0'){
        if(s[i] == ch){
            ans = &s[i];
        }
        i++;
    }
  
    return ans;
}

long AtoL(char* s){
  
    long ans = 0;
    int i=0;
    while(s[i]!='\0'){
        if(isdigit(s[i])){
            int temp = s[i] - '0';
            ans = ans*10 + temp;
        }
        else{
            break;
        }
        i++;
    }
  
    return ans;
}

int main(){
  
    char a[] = "helloworld";
    char b[] = "world";
    char c[] = "123.21";
  
    char *temp1 = strStr(a,b);
    if(temp1){
        cout<<temp1<<endl;
    }
  
    char* temp2 = strrchr(a,'o');
    cout<<temp2<<endl;
  
    long ans = AtoL(c);
    cout<<ans<<endl;
}```

Output :

Output: world orld 123