how repeat a string in language C

Question

how I do to repeat a string? something like "hello world" * 3 the output "hello world hello world hello world"

Answer 1

In your source code, without much processing, probably the easiest way is with:

#define HI "hello world"
char str[] = HI " " HI " " HI;

This will declare a string of the requested value:

"hello world hello world hello world"

If you want code that will do it, you can use something like:

char *repeatStr (char *str, size_t count) {
    if (count == 0) return NULL;
    char *ret = malloc (strlen (str) * count + count);
    if (ret == NULL) return NULL;
    strcpy (ret, str);
    while (--count > 0) {
        strcat (ret, " ");
        strcat (ret, str);
    }
    return ret;
}

Now keep in mind this can be made more efficient - multiple strcat operations are ripe for optimisation to avoid processing the data over and over ^(a) . But this should be a good enough start.

You're also responsible for freeing the memory returned by this function.

---

^(a) Such as with:

// Like strcat but returns location of the null terminator
//   so that the next myStrCat is more efficient.

char *myStrCat (char *s, char *a) {
    while (*s != '\0') s++;
    while (*a != '\0') *s++ = *a++;
    *s = '\0';
    return s;
}

char *repeatStr (char *str, size_t count) {
    if (count == 0) return NULL;
    char *ret = malloc (strlen (str) * count + count);
    if (ret == NULL) return NULL;
    *ret = '\0';
    char *tmp = myStrCat (ret, str);
    while (--count > 0) {
        tmp = myStrCat (tmp, " ");
        tmp = myStrCat (tmp, str);
    }
    return ret;
}

Answer 2

You could use sprintf.

char s[20] = "Hello";
char s2[20];
sprintf(s2,"%s%s%s",s,s,s);

Answer 3

http://ideone.com/5sNylW

#include <stdio.h>
#include <string.h>
int main(void) {
     char k[100];
     gets(k);
     int lk=strlen(k);
     int times;
     scanf("%d",&times);
     int tl= times*lk;
     int i,x=0;
        for(i=lk-1;i<tl;i++)
        {
        k[i+1]=k[x];
        x++;
        }
    for(i=0;i<tl;i++)
    {
    printf("%c",k[i]);
    }

     return 0;
}

Answer 4

You may try write own function. It will be work with single-length string also (ie duplication a single char). It use the function "strcat()" from the "string.h", so do not forget include this header.

char *
str_repeat(char str[], unsigned int times)
{
    if (times < 1)
        return NULL;

    char *result;
    size_t str_len = strlen(str);
    result = malloc(sizeof(char) * str_len + 1);

    while (times--) {
        strcat(result, str);
    }
    return result;
}

But, if you need only duplication of a string for print it, try macro

#define PRINT_STR_REPEAT(str, times) \
{ \
    for (int i = 0; i < times; ++i) \
        printf("%s", str); \
    puts(""); \
}

Results

PRINT_STR_REPEAT("-", 10); // ----------
puts(str_repeat("-", 10)); // ----------

PRINT_STR_REPEAT("$", 2); // $$
puts(str_repeat("$", 2)); // $$

PRINT_STR_REPEAT("*\t*", 10); // *   **  **  **  **  **  **  **  **  **  *
puts(str_repeat("*\t*", 10));  // *   **  **  **  **  **  **  **  **  **  *

PRINT_STR_REPEAT("*_*", 10); // *_**_**_**_**_**_**_**_**_**_*
puts(str_repeat("*_*", 10)); // *_**_**_**_**_**_**_**_**_**_*

Answer 5

Here's a way to repeat a string in C, N times.

That is have a string "abc" and I want a string of length 7 that is comprised of this string repeated.

N = 7; result: "abcabca"

 while(Index != N){

    repeatedString[Index] = oldString[Index%strlen(oldString)];
    Index++;
 }

Where repeated String would be "abcabca" at the end, and oldString is "abc".

Answer 6

I've made this function based on earlier answers in this post. I share it here because some of previous examples has been thrown me segfaults

const char* str_repeat(char* str, size_t times)
{
    if (times < 1) return NULL;
    char *ret = malloc(sizeof(str) * times + 1);
    if (ret == NULL) return NULL;
    strcpy(ret, &str);
    while (--times > 0) {
        strcat(ret, &str);
    }
    return ret;
}