Language exercise C

Question

Create a program that reads six integer values from the keyboard and then show on the screen the read values in reverse order. In reverse order, it would not be from the smallest to the smallest. How to do?

#include <stdio.h>
#include <stdlib.h>

int main()
{
   int i, num[6];
   printf("Digite 6 numeros inteiros.\n");
   for(i=0; i<6; i++) {
        printf("Digite o %d valor: ", (i+1));
    scanf("%d", &num[i]);
   }
   system("cls");
   for(i=0; i<6; i++) {

   system("pause");
   return 0;
}

It’s not homework, it’s from the book.

Answer 1

My interpretation of the reverse order would be as follows:

User enters the values: 1 2 3 4 5 6 The exit would be: 6 5 4 3 2 1

The code can be like this:

#include <stdio.h>
#include <stdlib.h>

int main()
{
   int i, num[6];
   printf("Digite 6 numeros inteiros.\n");

   for(i=0; i<6; i++) {
    printf("Digite o %d valor: ", (i+1));
    scanf("%d", &num[i]);
   }

   printf("Resultado:\n");
   for(i=5; i>=0; i--) {
    printf("%d\n", num[i]);
   }
   return 0;
}

Answer 2

First, your example does not compile, because it lacks a }. Look how he gets when properly devised:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i, num[6];
    printf("Digite 6 numeros inteiros.\n");
    for (i = 0; i < 6; i++) {
        printf("Digite o %d valor: ", i + 1);
        scanf("%d", &num[i]);
    }
    system("cls");
    for (i = 0; i < 6; i++) {
       system("pause");
       return 0;
    }

I suppose you’ve forgotten one printf and a } before the system("pause");. So that would be the code (printing in direct order):

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i, num[6];
    printf("Digite 6 numeros inteiros.\n");
    for (i = 0; i < 6; i++) {
        printf("Digite o %d valor: ", i + 1);
        scanf("%d", &num[i]);
    }
    system("cls");
    for (i = 0; i < 6; i++) {
        printf("O %d valor eh: ", num[i]);
    }
    system("pause");
    return 0;
}

You are reading the 6 numbers correctly. Then, the solution would be simple. I have two alternatives, choose the one you find best.

Alternative 1:

Just print the numbers on the screen in reverse order. For this, you iterate the array (in the second for) in reverse order:

for (i = 5; i >= 0; i--) {

Alternative 2:

You iterate the array in the correct order, but fill it in the reverse order:

    scanf("%d", &num[5 - i]);

Answer 3

A recursive solution :-)

#include <stdio.h>
#include <stdlib.h>

void le_imprime(int n);

int main(void) {
    puts("Digite 6 numeros inteiros.");
    le_imprime(6);
    puts("");
    return 0;
}

void le_imprime(int n) {
    int a;
    if (!n) return;
    if (scanf("%d", &a) != 1) {
        fprintf(stderr, "Erro de leitura.\nPrograma abortado.\n");
        exit(EXIT_FAILURE);
    }
    le_imprime(n - 1);
    printf("%d ", a);
}

Answer 4

A pornographic solution (not to show to anyone):

#include <stdio.h>

int main(int argc, char**allwaysnull) { int c;
  if( argc == 8 ){ return 0; }
  if( argc == 1 ){ printf("6 numeros inteiros.\n"); return main(2,NULL); }
  scanf("%d",&c);
  main(argc + 1,NULL); 
  printf("%d\n",c);
}

Update: at @pmg’s purist suggestion, I added the second main argument to (fraudulently) shut the warning -Wmain. The new version continues to be openly pornographic.