Question 58: There are 1, 2, 3, and 4 numbers. How many different three-digit numbers can be formed without repeated numbers? How many are they? Question 58: There are 1, 2, 3, and 4 numbers. How many different three-digit numbers can be formed without repeated numbers? How many are they? 
void main()
{ int i,j,k; printf("\n"); for(i=1;i<5;i++) {// The following is a triple loop, hundreds of for(j=1;j< 5;j++) {//Ten place for (k=1;k<5;k++) {// One place if (i!=k&&i!=j&&j!=k) {//Ensure i, j, k three places Different printf("%d%d%d ",i,j,k);
}
}
}
}
}