Bubble sort in C. Output is the same as input

Question

As a school assignment we are writing a bubble sort program in c. The code I wrote works. The only thing is that the output returns the input and doesn't return the swapped input. I'm kinda stuck. No matter what I do i either get an error or nothing changes. Does anybody know what is going wrong? Any help would be highly appreciated!!

#include <stdio.h>
#include <string.h>
#define MAXLENGTH 100      


void getString(char *str);  
void printResult(char *str);
int greaterThan(char ch1, char ch2); 
void swap(char *str, int index1, int index2);  


int main(void) {
int len;                  // length of the entered string
char str[MAXLENGTH];      // input should be no longer than MAXLENGTH


getString(str);
len = strlen(str);  // get length of the string, from sting.h
int j;
for (j = 0; j < len-j; j++) {  
    int i;
    for (i = 0; i < len-j; i++){    
        char ch1 = str[i];  
        char ch2 = str[i+1];    
        if (greaterThan(ch1, ch2)) {    
            swap(str, i, i+1);  // swap char 1
            swap(str, i, i+1);  // swap char 2
        }
    }
}
printResult(str);

return(0);
}



void getString(char *str) {    
    printf("Enter the string you would like to sort: ");  
    scanf("%s",str);   
    }


void printResult(char *str){    
    printf("Here is the sorted string: ");  
    printf("%s",str);   
}


int greaterThan(char ch1, char ch2){    
    return (ch1 > ch2);
}


void swap(char *str, int index1, int index2){   
    char h =  str[index1];  
    str[index1] = str[index2];  
    str[index2] = h;    
}

Answer 1

if (greaterThan(ch1, ch2)) {    
    swap(str, i, i+1);  // swap char 1
    swap(str, i, i+1);  // swap char 2
}

In this code you are swamping twice.

For Example: str = ['a','b','c'] swap(str,1,2) for first swap the " str " will be ['a','c','b'] and for the second swap " str " will be ['a','b','c']. That's why your Output is the same as input.

You Just Need To Call swap function only once.

if (greaterThan(ch1, ch2)) {    
    swap(str, i, i+1);
}

Answer 2

Here:

if (greaterThan(ch1, ch2)) {    
    swap(str, i, i+1);  // swap char 1
    swap(str, i, i+1);  // swap char 2
}

you are swapping twice while you should swap only once.

I was bad the below part of my answer's previous version is not bubble short:

Another problem is that you are using elements next to each other and you are not using i and j indexed ones to compare and swap. So you better should have something like this:

    if (greaterThan(str[i], str[j]))
        swap(str, i, j);

Answer 3

Try this:

getString(str);
len = strlen(str);  // get length of the string, from sting.h
int j;
for (j = 0; j < len-j; j++) {  
    int i;
    for (i = 0; i < len-j; i++){    
        char ch1 = str[i];  
        char ch2 = str[i+1];    
        if (greaterThan(ch1, ch2)) {    
            swap(str, i, i+1);  // swap char 1
        }
    }
}
printResult(str);

return(0);
}