How to use string substr function

Question

I want to make a program that will read some number in string format and output it like this  if the number is 12345 it should then output 12 23 34 45   I tried using the substr   function from the c   string library  but it gives me strange results - it outputs 1 23 345 45 instead of the expected result  Why     include  lt iostream gt   include  lt string gt   include  lt cstdlib gt  using namespace std  int main void        string a      cin  gt  gt  a      string b      int c       for int i 0 i lt a size  -1   i                b   a substr i i 1           c   atoi b c str             cout  lt  lt  c  lt  lt                 cout  lt  lt  endl      return 0

User · Answer

substr i j  means that you start from the index i  assuming the first index to be 0  and take next j chars  It does not mean going up to the index j

User · Answer

Possible solution without using substr     include lt iostream gt   include lt string gt   using namespace std    int main         string c  12345       int p 0       for int i 0 i lt c length   i              cout lt  lt c i           p             if  p   2    0  amp  amp  i    c length  -1                cout lt  lt     lt  lt c i               p

User · Answer

As shown here  the second argument to substr is the length  not the ending position   string substr   size t pos   0  size t n   npos   const  Generate substring Returns a string object with its contents initialized to a substring of the current object  This substring is the character sequence that starts at character position pos and has a length of n characters   Your line b   a substr i i 1   will generate  for values of i  substr 0 1    1 substr 1 2    23 substr 2 3    345 substr 3 4    45   since your string stops there    What you need is b   a substr i 2   You should also be aware that your output will look funny for a number like 12045  You ll get 12 20 4 45 due to the fact that you re using atoi   on the string section and outputting that integer  You might want to try just outputing the string itself which will be two characters long  b   a substr i 2   cout  lt  lt  b  lt  lt   quot   quot    In fact  the entire thing could be more simply written as   include  lt iostream gt   include  lt string gt  using namespace std  int main void        string a      cin  gt  gt  a      for  int i   0  i  lt  a size   - 1  i            cout  lt  lt  a substr i 2   lt  lt   quot   quot       cout  lt  lt  endl      return 0

User · Answer

Another interesting variant question can be   How would you make  12345  as  12 23 34 45  without using another string   Will following do       for int i 0  i  lt  a size  -1    i                  b   a substr i  2           c   atoi  a substr i  2   c str             cout  lt  lt  c  lt  lt

User · Answer

You can get the above output using following code in c   include lt stdio h gt   include lt conio h gt   include lt string h gt  int main       char  str    clrscr      printf   n Enter the string      gets str     for int i 0 i lt strlen str -1 i            for int j i j lt  i 1 j          printf   c  str j        printf   t          getch      return 0

User · Answer

If I am correct  the second parameter of substr   should be the length of the substring  How about  b   a substr i 2

User · Answer

Possible solution with string view  void do it with string view  void         std  string a    12345         for   std  string view v   a    v size   - 1  v remove prefix  1             std  cout  lt  lt  v substr  0  2    lt  lt           std  cout  lt  lt  std  endl

[c++] How to use string.substr() function?

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