在 C 的 for 循环中使用 strcmp 和 printf

Question

I have a question which I like to demonstrate with a piece of code. Having the following code:

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

int main()
{
    char *fruit[] = {
        "apricot"
    ,   "banana"
    ,   "pineapple"
    ,   "apple"
    ,   "persimmon"
    ,   "pear"
    ,   "blueberry"
    };
    char *temp;
    int a,b,x,y;

    for (a=0;a<6;a++)
            for(b=a+1;b<7;b++)
                y=strcmp(*(fruit+a),*(fruit+b));
                printf("strcompare value is %x\n",y);
                if(strcmp(*(fruit+a),*(fruit+b)) > 0)
                {
                    temp = *(fruit+a);
                    *(fruit+a) = *(fruit+b);
                    *(fruit+b) = temp;
                }

    for (x=0;x<7;x++)
        puts(fruit[x]);

    return (0);
}

As you can see, the printf output is only executes ones. And the list of fruit is not sorted. When I make a slight change to the code, exclude the use of variable y, as in the below code block:

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

int main()
{
    char *fruit[] = {
        "apricot"
    ,   "banana"
    ,   "pineapple"
    ,   "apple"
    ,   "persimmon"
    ,   "pear"
    ,   "blueberry"
    };
    char *temp;
    int a,b,x,y;

    for (a=0;a<6;a++)
            for(b=a+1;b<7;b++)
                //y=strcmp(*(fruit+a),*(fruit+b));
                printf("strcompare value is %x\n",strcmp(*(fruit+a),*(fruit+b)));
                if(strcmp(*(fruit+a),*(fruit+b)) > 0)
                {
                    temp = *(fruit+a);
                    *(fruit+a) = *(fruit+b);
                    *(fruit+b) = temp;
                }

    for (x=0;x<7;x++)
        puts(fruit[x]);

    return (0);
}

Now we see this output:

The printf is repeated but the sorting is not correct yet. Removing the printf command as in the code below:

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

int main()
{
    char *fruit[] = {
        "apricot"
    ,   "banana"
    ,   "pineapple"
    ,   "apple"
    ,   "persimmon"
    ,   "pear"
    ,   "blueberry"
    };
    char *temp;
    int a,b,x,y;

    for (a=0;a<6;a++)
            for(b=a+1;b<7;b++)
                //y=strcmp(*(fruit+a),*(fruit+b));
                //printf("strcompare value is %x\n",strcmp(*(fruit+a),*(fruit+b)));
                if(strcmp(*(fruit+a),*(fruit+b)) > 0)
                {
                    temp = *(fruit+a);
                    *(fruit+a) = *(fruit+b);
                    *(fruit+b) = temp;
                }

    for (x=0;x<7;x++)
        puts(fruit[x]);

    return (0);
}

This code is giving the requested output:

Now i have the following questions:

1. why is the printf command in the first attemp not repeated and the sorting not happening?
2. what is wrong using a interger var to accept the strcmp outcome and use that var afterwards?
3. why does leaving out the printf function has a positive effect on the outcome?

Answer 1

If one loop contains more than 1 statement, you need to surround the statements by curly braces to create a compound statement:

for (a=0;a<6;a++) 
{
    for(b=a+1;b<7;b++)
    {
        //y=strcmp(*(fruit+a),*(fruit+b));
        printf("strcompare value is %x\n",strcmp(*(fruit+a),*(fruit+b)));

        if(strcmp(*(fruit+a),*(fruit+b)) > 0)
        {
            temp = *(fruit+a);
            *(fruit+a) = *(fruit+b);
            *(fruit+b) = temp;
        }
    }
}

Else if you do:

for (a=0;a<6;a++) 
    for(b=a+1;b<7;b++)
        //y=strcmp(*(fruit+a),*(fruit+b));
        printf("strcompare value is %x\n",strcmp(*(fruit+a),*(fruit+b)));

        if(strcmp(*(fruit+a),*(fruit+b)) > 0)
        {
            temp = *(fruit+a);
            *(fruit+a) = *(fruit+b);
            *(fruit+b) = temp;
        }

the if statement of:

 if(strcmp(*(fruit+a),*(fruit+b)) > 0)
 {
     temp = *(fruit+a);
     *(fruit+a) = *(fruit+b);
     *(fruit+b) = temp;
 }

is executed after the nested loops, but not inside the inner one, which is equivalent to:

for (a=0;a<6;a++) 
{
    for(b=a+1;b<7;b++)
    {
        //y=strcmp(*(fruit+a),*(fruit+b));
        printf("strcompare value is %x\n",strcmp(*(fruit+a),*(fruit+b)));
    }
}

if(strcmp(*(fruit+a),*(fruit+b)) > 0)
{
     temp = *(fruit+a);
     *(fruit+a) = *(fruit+b);
     *(fruit+b) = temp;
}