Getting wrong output while trying to sort information first by age and in case of same age then alphabetically

Question

So I have to sort a list of people's information by their ages. In case there are people of the same ages, I have to sort them by their names alphabetically.

Here's my code:

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

struct people{
    char name[30];
    int age;
};

int main(){
    int n, i, j, min, tmp1;
    scanf("%d", &n);
    struct people person[n], temp;

    for(i = 0; i < n; i++){
        scanf("%s%d", person[i].name, &(person[i].age));
    }
    
    // SELECTIONN SORT
    for(i = 0; i < n - 1; i++){
        min = i;
        for(j = i + 1; j < n; j++){
            if (person[j].age < person[i].age ||
                strcmp(person[j].name,person[min].name) < 0 && person[j].age == person[min].age){
                min = j;
            }
        }
        if(min != i){
            temp.age = person[i].age;
            person[i].age = person[min].age;
            person[min].age = temp.age;

            strcpy(temp.name, person[i].name);
            strcpy(person[i].name, person[min].name);
            strcpy(person[min].name, temp.name);
        }
    }

    for(i = 0; i < n; i++){
        printf("%s %d\n", person[i].name, (person[i].age));
    }
}

In almost all of the cases I tried, the code works, however, on this certain input I get "Mary 15" before "Anna 15" and I have no idea why, here's the input:

5
Gilbert 35
Anna 35
Anna 15
Mary 15
Joseph 40

Answer 1

I think the compare you're doing isn't right.

Change:

person[j].age < person[i].age

Into:

person[j].age < person[min].age

And, as I mentioned in my top comment, the swap can be simplified.

And, we can split up the if to make it clearer with no loss of speed.

---

Here is the corrected code. It is annotated:

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

struct people {
    char name[30];
    int age;
};

int
main(void)
{
    int n, i, j, min, tmp1;
#if 1
    int dif;
#endif

    scanf("%d", &n);

    struct people person[n], temp;
    for (i = 0; i < n; i++) {
        scanf("%s%d", person[i].name, &(person[i].age));
    }

    // SELECTIONN SORT
    for (i = 0; i < n - 1; i++) {
        min = i;
        for (j = i + 1; j < n; j++) {
#if 0
            if (person[j].age < person[i].age ||
                strcmp(person[j].name, person[min].name) < 0 &&
                person[j].age == person[min].age) {
                min = j;
            }
#else
            dif = person[j].age - person[min].age;

            // ages are out-of-sort
            if (dif < 0) {
                min = j;
                continue;
            }

            // ages are in-sort
            if (dif > 0)
                continue;

            // compare names only if ages are the same
            dif = strcmp(person[j].name, person[min].name);
            if (dif < 0) {
                min = j;
                continue;
            }
#endif
        }

        if (min != i) {
// we can simplify this ...
#if 0
            temp.age = person[i].age;
            person[i].age = person[min].age;
            person[min].age = temp.age;

            strcpy(temp.name, person[i].name);
            strcpy(person[i].name, person[min].name);
            strcpy(person[min].name, temp.name);
#else
            temp = person[i];
            person[i] = person[min];
            person[min] = temp;
#endif
        }
    }

    for (i = 0; i < n; i++) {
        printf("%s %d\n", person[i].name, (person[i].age));
    }
}

---

In the code above, I've used cpp conditionals to denote old vs. new code:

#if 0
// old code
#else
// new code
#endif

#if 1
// new code
#endif

Note: this can be cleaned up by running the file through unifdef -k

---

Here is the output of the corrected code:

Anna 15
Mary 15
Anna 35
Gilbert 35
Joseph 40