strings concatenation issues in c

Question

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    int x,y;
    char s1[30],s2[30];
    printf("Enter string 1:");
    scanf("%s",s1);
    printf("Enter string 2:");
    scanf("%s",s2);
    x=sizeof(s1),y=sizeof(s2);
    char cs1[x+y+1];
    char cs2[x+y+1];
    for (int i = 0; i < x; i++)
    {
        cs1[i]=s1[i];
    }
    for (int i =x; i < (x+y); i++)
    {
        cs1[i]=s2[i];
    }
    for (int i = 0; i < (y); i++)
    {
        cs2[i]=s2[i];
    }
    for(int i=y;i<(x+y);i++)
    {
        cs2[i]=s1[i];
    }
    cs1[x+y]='\0';
    cs2[x+y]='\0';
    printf("string 1+string 2 is:%s",cs1);
    printf("\nstring 2+ string 1 :%s",cs2);
    
    
    
    

 





    return 0;
}

i tried to concatenate two strings without using the inbuilt functions to do this, can you please point the error out? this was giving the strings as they are i mean to say it is printing s1 string in place of cs1 and s2 in place of cs2

Answer 1

These assignments:

 x=sizeof(s1),y=sizeof(s2);

do not make a sense because the assigned values do not represent lengths of entered strings.

You need to write:

#include <string.h>

//...

size_t x,y;
char s1[30],s2[30];
printf("Enter string 1:");
scanf("%s",s1);
printf("Enter string 2:");
scanf("%s",s2);
x = strlen(s1), y = strlen(s2);
//...

These for loops:

for (int i =x; i < (x+y); i++)
{
    cs1[i]=s2[i];
}

//...

for(int i=y;i<(x+y);i++)
{
    cs2[i]=s1[i];
}

are incorrect. You need to write:

for ( size_t i = 0; i < y; i++)
{
    cs1[i + x] = s2[i];
}

//...

for( size_t i = 0; i < x; i++)
{
    cs2[i + y ] = s1[i];
}

Answer 2

Oh well, an answer got accepted just before I could post my version, but just for reference I'll paste it anyway.

As others pointed out, there were a number of errors in your code:

• sizeof(s) would always yield 30, you have to use a function defined by yourself if you want to easily count the length of a string
• inside the various for, you were using the wrong index when copying the string
• while I was at it, I changed the scanf to fgets so that you could accept strings with spaces too. And I added a #define MAX_LENGTH 30 at the top, so that you could easily re-purpose the program for shorter/longer inputs

Anyway, here's the code

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

#define MAX_LENGTH 30   /* use defines instead of repeating the same number by hand */

int myStrLen(char *s, int max_len) {
  /* this little function counts the lenght of the passed string, up to max_len */
  int len = 0;
  for (int i = 0; i < max_len; i++) {
    if (s[i] != '\0' && s[i] != '\n') {
      len++;
    } else {
      break;
    }
  }
  return len;
}

int main() {
  int x, y;
  char s1[MAX_LENGTH], s2[MAX_LENGTH];

  printf("Enter string 1:");
  fgets(s1, MAX_LENGTH, stdin); /* using fgets instead of scanf allows reading strings containing spaces */
  //scanf("%s",s1);
  
  printf("Enter string 2:");
  fgets(s2, MAX_LENGTH, stdin);
  //scanf("%s",s2);

  x = myStrLen(s1, sizeof(s1));
  y = myStrLen(s2, sizeof(s2));
  printf("string1 length: %d\nstring2 length: %d\n", x, y);

  char cs1[x + y + 1];
  char cs2[x + y + 1];

  for (int i = 0; i < x; i++) {
    cs1[i] = s1[i];
  }
  for (int i = 0; i < y; i++) {
    cs1[i+x] = s2[i];   // nb: (i+x) instead of i
  }
  for (int i = 0; i < y; i++) {
    cs2[i] = s2[i];
  }
  for (int i = 0; i < x; i++) {
    cs2[i+y] = s1[i];   // // nb: (i+y) instead of i
  }

  cs1[x + y] = '\0';
  cs2[x + y] = '\0';

  printf("string1+string2 is:%s\n", cs1);
  printf("string2+string1 is:%s\n", cs2);
  return 0;
}

Answer 3

x=sizeof(s1),y=sizeof(s2); sizeof does not give you the length of the string

Use function strlen instead.

Your for loops are also wrong

    for (size_t i = 0; i < x; i++)
    {
        cs1[i]=s1[i];
    }
    for (int i = x; i < (x+y); i++)
    {
        cs1[i]=s2[i - x];
    }
    for (int i = 0; i < (y); i++)
    {
        cs2[i]=s2[i];
    }
    for(int i=y;i<(x+y);i++)
    {
        cs2[i]=s1[i - y];
    }

Answer 4

Try this, that work for me and I created a function "my_strlen" to get the size of your string

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

    int my_strlen(char *str)
    {
        int i;

        for (i = 0; str[i] != '\0'; i++);
        return (i);
    }

    int main()
    {
        int x,y;
        char s1[30],s2[30];
        printf("Enter string 1:");
        scanf("%s",s1);
        printf("Enter string 2:");
        scanf("%s",s2);
        x=my_strlen(s1),y=my_strlen(s2);
        char cs1[x+y+1];
        char cs2[x+y+1];
        for (int i = 0; s1[i] != '\0'; i++)
        {
            cs1[i]=s1[i];
        }
        for (int i = 0; s2[i] != '\0'; i++)
        {
            cs1[i + x] = s2[i];
        }
        for (int i = 0; s2[i] != '\0'; i++)
        {
            cs2[i] = s2[i];
        }
        for(int i = 0; s1[i] != '\0'; i++)
        {
            cs2[i + y] = s1[i];
        }
        cs1[x+y]='\0';
        cs2[x+y]='\0';
        printf("string 1+string 2 is:%s",cs1);
        printf("\nstring 2+ string 1 :%s",cs2);
        return (0);
    }