The first character in both string won't swap in C [closed] - c

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#include <stdio.h>
#define SIZE 101
void swap(char *a, char *b);
int main(void) {
char string1[SIZE];
char string2[SIZE];
printf("please enter string 1 :");
scanf("%s", string1);
printf("please enter string 2 :");
scanf("%s", string2);
swap(string1, string2);
printf("string 1 is %s, string 2 is %s\n", string2, string1);
}
void swap(char *a, char *b) {
int i;
char temp[101];
for (i = 0; i < SIZE; i++) {
temp[i] = *a;
*a = *b;
*b = temp[i];
}
}
When I give inputs to both string1 and string2 lets say "yes" and "hello", it will print string1 is yello and string2 is hes. I've tried to modify by changing *b to *[b+1] and *a to *[a+1] and it gets the first character to work but now the second character won't swap.
EDIT
Also I've tried another function but the problem is still there.
void swap(char* a, char* b)
{
char temp;
temp=*a;
*a=*b;
*b=temp;
a++;
b++;
}

Answer 1

Your swap function is wrong:
Here is the corrected version:
void swap(char* a, char* b)
{
int i; char temp;
for (i = 0; i<SIZE; i++)
{
temp = a[i];
a[i] = b[i];
b[i] = temp;
}
}
you don't need a temp array, just one char is enough for the temporary.
you need to access the different chars of the input a and b, and not only the first one.
BTW: here is a better version of swap where you pass the size as parameter:
void swap(char* a, char* b, int size)
{
int i; char temp;
for (i = 0; i < size; i++)
{
temp = a[i];
a[i] = b[i];
b[i] = temp;
}
}

Answer 2

Actually only the first characters of your strings is swapped(which makes sense as mentioned in other answers), you don't see this because you change the order of printing with
printf("string 1 is %s, string 2 is %s\n", string2, string1);
^^^^^^^^^^^^^^^
Here you are always just swapping the first character since you a and b always point to first element.
for(i=0; i<SIZE; i++)
{
temp[i]= *a;
*a=*b;
*b=temp[i];
}
you can use array subscript
int i; char temp;
for (i = 0; i < SIZE; i++)
{
temp = a[i];
a[i] = b[i];
b[i] = temp;
}

Answer 3

There are multiple problems in your code:
you print the strings in the wrong order
you only swap the first character, and you do this SIZE times. SIZE is odd so you see it swapped, the previous bug makes it look like the other characters were swapped. If SIZE were even, you would not swap anything and the previous bug would let you erroneously believe everything is fine...
Less important, but worth mentioning:
you do not check the return values of scanf()
you do not return 0 at the end of main().
Here is a corrected and improved version:
#include <stdio.h>
#define SIZE 101
void swap(char *a, char *b, int size) {
for (int i = 0; i < size; i++) {
char temp = a[i];
a[i] = b[i];
b[i] = temp;
}
}
int main(void) {
char string1[SIZE];
char string2[SIZE];
printf("please enter string 1 :");
if (scanf("%s", string1) != 1)
return 1;
printf("please enter string 2 :");
if (scanf("%s", string2) != 1)
return 1;
swap(string1, string2, SIZE);
printf("string 1 is %s, string 2 is %s\n", string1, string2);
return 0;
}

Answer 4

Try to use parentheses like *(a+1) instead of bracket *[b+1]. In your code
change the following
for(i=0; i<SIZE; i++)
{
temp[i]= *a;
*a=*b;
*b=temp[i];
}
with
for(i=0; i<SIZE; i++)
{
temp[i] = *(a+i);
*(a+i) = *(b+i);
*(b+i) = temp[i];
}
Final code is here:
#include <stdio.h>
#define SIZE 101
void swap(char* a, char* b);
int main(void)
{
char string1[SIZE]; char string2[SIZE];
printf("please enter string 1 :");
scanf("%s",string1);
printf("please enter string 2 :");
scanf("%s",string2);
swap(string1, string2);
printf("string 1 is %s, string 2 is %s\n",string1,string2);
return 0;
}
void swap(char* a, char* b)
{
int i; char temp[101];
for(i=0; i<SIZE; i++)
{
temp[i] = *(a+i);
*(a+i) = *(b+i);
*(b+i) = temp[i];
}
}