Functions works only 1 time

Question

I've encountered a problem with my code where the function I made rotate_left that's supposed to take the first word in a given string and puts it at the end of that string and that function works but when it tried to activate it twice it doesn't do anything other than printing the same result the first function printed anyone got any ideas about it?

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#define MAX 80
void rotate_left(char str[])
{
    int j = 0;
    int i = 0;
    char Temp[MAX];
    char Temp2[MAX];
    while (str[i] != ' ')
    {
        i++;
    }
    Temp[i] = '\0';
    strncpy(Temp, str, i);
    strcat(str, " ");
    while (str[i] != '\0')
    {
        Temp2[j] = str[i];
        i++;
        j++;
    }
    Temp2[j] = '\0';
    strcat(Temp2, Temp);
    printf("%s\n", Temp2);
}

int main()
{
    char str[MAX];
    char Temp2[MAX];
    printf("Enter Your String To Swtich The :  ");  
    gets(str);
    rotate_left(str);
    rotate_left(str);
    rotate_left(str);
    return 0;
}  

Answer 1

Your code has issues:

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#define MAX 80
void rotate_left(char str[])
{
    int j = 0;
    int i = 0;
    char Temp[MAX];
    char Temp2[MAX];
    while (str[i] != ' ')
    {
        i++;
    }

in the code below you are having a security leak and a potential problem because you have temp variables in the stack and you are touching these without boundary checks: Example of a buffer overflow leading to a security leak

you need to write code with boundary checks especially when the variable is in the stack:

while (i < MAX /*or i < sizeof(str)*/ && str[i] != ' ' && str[i] != '\0' /*Null check also?*/ )
{
    i++;
}

If you call this method with a string without space in it then god knows what will it result,

There are other issues as well like "strncpy(str, Temp2, strlen(Temp2) + 1);" this is not how this method is intended to be called as it should be "strncpy(str, Temp2, sizeof(str));": https://linux.die.net/man/3/strncpy

Let me write you sample code it will be faster for you to track some of the missing checks:

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

#define MAX 80

/* just your code with safety checks so you can track why it fails */
int rotate_left(char str[], const size_t inputSize)
{
    int j = 0;
    int i = 0;
    char Temp[MAX];
    char Temp2[MAX];

    while (i < inputSize && str[i] != ' ' && str[i] != '\0')
    {
        i++;
    }

    if (i == inputSize || str[i] == '\0')
    {
        // string without any space in it so no need to rotate?
        return 0;
    }

    if (i + 1/*+1 to include null*/ >= MAX) {

        // We dont have enough memory to handle this request
        return -1;
    }

    strncpy(Temp, str, i);
    Temp[i] = '\0';

    ++i;

    while (i < inputSize && j < MAX && str[i] != '\0')
    {
        Temp2[j] = str[i];
        i++;
        j++;
    }
    if (i == inputSize) {
        // String is not null terminated?
        return -1;
    }

    if (j + 2 /*Include space and null character*/ >= MAX) {
        // We dont have enough memory to handle this request
        return -1;
    }

    Temp2[j] = ' ';
    Temp2[j + 1] = '\0';
    strncat(Temp2, Temp, sizeof(Temp2));
    strncpy(str, Temp2, inputSize); //<====== copies the string
    printf("%s\n", str);

    return 0;
}

/* bit more optimization */
errno_t rotate_left_optimized(char str[], const size_t inputSize)
{
    errno_t lastCall;
    char temp[MAX];
    int i = 0;

    while (i < inputSize && str[i] != ' ' && str[i] != '\0')
    {
        i++;
    }

    if (i == inputSize || str[i] == '\0')
    {
        // string without any space in it so no need to rotate?
        return 0;
    }
    const size_t inputLen = strnlen(str, inputSize);

    if (i + 1 /* Include lazy space character */>= sizeof(temp)) {
        // We dont have enough memory to handle this request
        return -1;
    }
    // hidden assert(str[i] == ' ');

    temp[0] = ' ';
    memcpy(temp + 1, str, i);
    memmove(str, str + i + 1, inputLen);
    lastCall = strncat_s(str, inputSize, temp, i + 1);
    if (!lastCall)
    {
        return lastCall;
    }
    return 0;
}

int main()
{
    char str[MAX] = "Enter Your String To Switch The";

    for (int i = 0; i < 7; i++) {
        if (rotate_left_optimized(str, MAX)) {
            perror("failed to rotate");
            exit(EXIT_FAILURE);
        }

        printf("%s\n", str);
    }
    return 0;
}

Answer 2

You have two bugs in these codes : First you must copy the rotated string in the passed one, printing the result is not sufficient. Next you must remove the space at the beginning of the extracted word otherwise the new string start with a space.

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>

#define MAX 80

void rotate_left(char str[])
{
    int j = 0;
    int i = 0;
    char Temp[MAX];
    char Temp2[MAX];
    
    // If the first space is not removed (see below), the next time
    // the function is called, this loop stops immediately. It's why
    // the second rotation didn't occur
    while (str[i] != ' ')
    {
        i++;
    }
    Temp[i] = '\0';
    strncpy(Temp, str, i);
    strcat(str, " ");
    i++; //<====== removes the space
    while (str[i] != '\0')
    {
        Temp2[j] = str[i];
        i++;
        j++;
    }
    Temp2[j] = '\0';
    strcat(Temp2, Temp);
    strncpy(str, Temp2, strlen(Temp2) + 1); //<====== copies the string
    printf("%s\n", str);
}

int main()
{
    
    char str[MAX] = "Enter Your String To Switch The";
    char Temp2[MAX];

    for (int i=0; i<7; i++) rotate_left(str);

    return 0;
}

Output :

Your String To Switch The Enter
String To Switch The Enter Your
To Switch The Enter Your String
Switch The Enter Your String To
The Enter Your String To Switch
Enter Your String To Switch The
Your String To Switch The Enter

I didn't handle special cases (if there is no space in the provided string for instance) and I removed the interactive dimension (gets) for the example.