Pointers and cstring beginner troubles

Question

I have a problem with the function replace. What I want to accomplish is to replace some special characters, but I haven't written the code yet. So in the replace function we can at this moment just say that the function should print line for line the way I have tried to write. Can someone please correct this function? I can’t really get it

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

struct list_el {
 char *ord;
 int num;
    struct list_el *prev;
 struct list_el *next;
};

typedef struct list_el item;
struct list_el *head, *tail; /*Double linked list that makes it easier to add a element to the end of the FIFO list*/

void addNode(struct list_el *curr);
void readFile();
void print();
void replace();
void random();
void len();

int antE = 0;

int randint(int max) 
{ 
 int a = (max*rand()/(RAND_MAX+1.0));
 return a;
}

int main(int argc, char *argv[]) {
 item *curr;

 struct list_el *pa;

 if(argc == 3) {
  readFile();
 }
 if(argc == 1) {
  printf("Too few arguments, must bee 3");
 } else if(strcmp(argv[1], "print") == 0) {
  print();
 } else if(strcmp(argv[1], "random") == 0)  {
  random();
 } else if(strcmp(argv[1], "replace") == 0)  {
  replace();
 } else if(strcmp(argv[1], "remove") == 0)  {
  printf("Random kommando kalt");
 } else if(strcmp(argv[1], "len") == 0)  {
  len();
 } else {
  printf("Not a valid command");
 }

 if(argc == 3) {
  free(curr);
 }
}

void addNode(struct list_el *curr) {
 if(head == NULL) {
  head = curr;
  curr->prev = NULL;
 } else {
  tail->next = curr;
  curr->prev = tail;
 }

 tail = curr;
 curr->next = NULL;
}

void readFile()
{
 FILE *f = fopen("tresmaa.txt", "r");

 if(f == 0) {
  printf("Could not open file");
  exit(8);
 }
 item *curr;

 if(f != NULL) {
  int antE = 0;
  head = NULL;
  char buffer[300];

  while(fgets(buffer, 300-1,f) != NULL) {
    curr = (item*)malloc(sizeof(item));
    curr->ord = malloc(300);
    curr->num = antE;
    strcpy(curr->ord, buffer);
    antE++;
    addNode(curr);
   }
  }
 fclose(f);
 }

/*Traverserer listen og printer ut linje for lije
 */
void print()
{
 item *curr;
 printf("Print text:\n");
 for(curr = head; curr != NULL; curr = curr->next) {
   printf("%s", curr->ord);
 }
}

/*Printer ut en tilfeldig setning
 */
void random()
{
 item *curr;
 int anum = randint(antE);
 for(curr = head; curr != NULL; curr = curr->next) {
  if(curr->num == anum) {
   printf("Print a random line:\n%s", curr->ord);
  }
 }
}

void replace()
{
 item *curr;
 int i;
 char tmp[300];

 printf("Replace vowels ...\n");
 printf("... with vowel 'a'\n");

 for(curr = head; curr != NULL; curr = curr->next) {
  strcpy(tmp, curr->ord);

  for(i = 0; i < strlen(tmp); i++) {
   printf("%s", tmp[i]);
  }
 }
}

void len()
{
 item *curr;
 long nc;
 int i;
 nc = 0;

 for(curr = head; curr != NULL; curr = curr->next) {
  nc += strlen(curr->ord);
 }
 printf("The text is %d characters long", nc);
}

Answer 1

If you just want to print the lines you can do it without the copying and extra loop:

for(curr = head; curr != NULL; curr = curr->next) {
   printf("%s\n", curr->ord);
}

Your current code doesn't work because you tell printf with the %s format that its argument will be a string (aka. a pointer to a zero-terminated sequence of characters), but then you give it a single character, not such a pointer.