How to use malloc in C?

well basically the design is not good but you can make it work like that if you just
assign the increment values correctly no need to have fixed string length
you can do variable string length as long as you take care not to overflow your malloc size

#include <stdio.h> 
#include <conio.h> 
#include <stdlib.h> 

int main(void) 
{ 
   char * pi; 
  int i,r,len[5]= {0},wen =0 ,foo=0; 
   puts("start"); 
   pi = (char *) malloc(50 * sizeof(char)); 
    
    
  for(i = 0; i < 5; i++) 
  { 
  r = scanf("%s%n",&pi[wen],&len[i]); //len[i] will hold the length of input
    if(r != 1) 
    break;
	if(i==0)
    	wen = wen + len[i]+ 1; //first time we need to add a 0 terminator
        else
	wen = wen + len[i];    // from second time no need coz it will point right
  
} 
      i = 0; 
      while(i < 5) 
      { 
        printf("%s",&*(pi + foo )); 
        putchar('\n'); 
	if(i==0)
             foo = foo + len[i] + 1; //same as above skip 0 terminator
	else
	foo = foo + len[i];    // no need second time onwards
	i++;
          } 
    
          free(pi); 
          puts("Done!"); 
          
      


  getch(); 
  return 0; 

}

output

start
rrrrrrrrrrrrrrrrrrrrr
ttttttttttttttttttttttt
yyyyyy
zest
malloc
rrrrrrrrrrrrrrrrrrrrr
ttttttttttttttttttttttt
yyyyyy
zest
malloc
Done!

but ill advise you get a c book or c++ book and leaf through them

have fun