nested for loops ending sooner than expected

Question

My code:

#include <stdio.h>
#include <math.h>

void block(int r, char a, char b);

int main(){
  block(2, '+', '-');
}

void block(int r, char a, char b){
  int i;
  char x = a;
  char y = b;
  for (i = 1; i <= r; i++){
    if ( i%2 == 1){
      for (i = 1; i <= r; i++){
        printf("%c", x);
      }
      for (i = 1; i <= r; i++){
        printf("%c", y);
      }
    } else
    {
      for (i = 1; i <= r; i++){
        printf("%c", x);
      }
      for (i = 1; i <= r; i++){
        printf("%c", y);
      }
    }
    printf("\n");
  }
  return;
}

intended output:

++--
--++

what I get instead:

++--

Nothing prints after the first line. For instance for r = 5 it prints the first line +++++----- correctly but doesn't print the remaining lines of the solution.

correct solution:

+++++-----
-----+++++
+++++-----
-----+++++
+++++-----

See also hints from [that](https://stackoverflow.com/a/50189411/841108) answer — Basile Starynkevitch, May 06 '18 at 07:34
... and that would be ok in your case if you'd declared the counter locally, inside the `for`. — Jens Gustedt, May 06 '18 at 07:34
You might like to read this: [How to debug small programs](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) — alk, May 06 '18 at 07:36
As an aspiring programmer, debugging is one of the most important skills you need to learn. The article linked by alk above has some great tips to get you started. — Code-Apprentice, May 06 '18 at 07:41
@rustyx Care to make an answer? Just to get this out of the list of unanswered questions. — Yunnosch, May 06 '18 at 07:42
@alk thank you for the useful article, I am going to start on it so that I don't encounter a similar problem again :) — A0sXc950, May 06 '18 at 07:43
Also, you're duplicating too much code. You don't need `x` and `y` or loops within `if`-`else` - just swap `a` and `b` for each line and be done with it. — Antti Haapala -- Слава Україні, May 06 '18 at 08:30

A0sXc950 · Accepted Answer · 2018-05-06T07:50:43.883

Thanks to @rustyx

This ended up doing the trick for me.

#include <stdio.h>
#include <math.h>

void block(int r, char a, char b);

int main(){
  block(5, '+', '-');
}

void block(int r, char a, char b){
  int i;
  char x = a;
  char y = b;
  for (i = 1; i <= r; i++){
    if ( i%2 == 1){
      int j;
      for (j = 1; j <= r; j++){
        printf("%c", x);
      }
      for (j = 1; j <= r; j++){
        printf("%c", y);
      }
    }
    else{
      int k;
      for (k = 1; k <= r; k++){
        printf("%c", y);
      }
      for (k = 1; k <= r; k++){
        printf("%c", x);
      }
    }
    printf("\n");
  }
  return;
}

giving this result:

+++++-----
-----+++++
+++++-----
-----+++++
+++++-----

Please try for some more consistent indentation. The one from the edited question maybe ... — Yunnosch, May 06 '18 at 07:44

nested for loops ending sooner than expected

1 Answers1