Assignment and Conditional check in C

Question

I came across this below program and I don't understand the output.

Can someone please shed some light on it?

#include <stdio.h>

int main()
{
  int i=1,j=1;
  for(;j;printf("%d %d\n",i,j))
  j=i++ <=5;
  return 0;
}

And its output is:

2 1
3 1
4 1
5 1
6 1
7 0

Answer 1

#include <stdio.h>

int main()
{
  int i=1,j=1;

  //for(initialisation; condition; operations)
  // here no initialisation, 
  // 1. condition is j, if j is true 
  // 2. then it will execute block statements 
  // 3. then finally it execute operations, here printf
  // 4. again check step 1.

  for(;j;printf("%d %d\n",i,j))
  j=i++ <=5;  // j = (i <= 5); i++;
  return 0;
}

Your question can be simplified as follows

#include <stdio.h>
int main()
{
  int i=1,j=1;
  while(j) {   
    j = (i++ <=5);
    printf("%d %d\n",i,j);
  }
  return 0;
}