# Knowing which way to iterate the for loop C

I want the code to automatically know which way to iterate through the loop without manually adding the '>' or '<' sign. I am using the logic that if the setup part of the loop is smaller than the value in the test expression, then the sign used will '<' and will be '>' vice versa.

The current way I have gone around this is by wrapping the for loop in an if statement, however this looks incredibly bulky and I feel there must be a better way.

The following is the code I am currently using:

i = -1;

if ((i*i*i)<(i * i * (i + i + i + i + i))){
for (integer = i * i * i; integer < i * i * (i + i + i + i + i);integer += i * i * i * i * i) {
printf("%d",integer);
printf("\n");
}
}
else {
for (integer = i * i * i; integer > i * i * (i + i + i + i + i);integer += i * i * i * i * i) {
printf("%d",integer);
printf("\n");
}
}


And here is an example which looks simpler:

if (-1<-5){
for (integer = -1; integer < -5;integer += -1) {
printf("%d",integer);
printf("\n");
}
}

else{
for (integer = -1; integer > -5;integer += -1) {
printf("%d",integer);
printf("\n");
}
}

• Why wouldn't you want to use the second version? – Mast Nov 16 '17 at 17:24
• Do both solve exactly the same problem? I highly doubt it. – Mast Nov 16 '17 at 17:24
• regarding: if (-1<-5){ This will NEVER be true However, this: if ((i*i*i)<(i * i * (i + i + i + i + i))){ will be true if 'i' is >0 and false otherwise – user3629249 Nov 18 '17 at 18:12
• Welcome to Code Review! This question is incomplete. To help reviewers give you better answers, please edit to add sufficient context to your question. The more you tell us about what your code does, the easier it will be for reviewers to help you. Questions should include a description of what the code does. – Toby Speight Nov 23 '17 at 10:28

You have a really complicated example with variables, and a simpler one with literals. The literal one is only going to use one branch. So let's do a simple one with variables. Let's say you want to iterate from a to b, but you don't know which is larger. Well, first of all, unless I'm missing something, if a>b, then you'll want integer -= increment in the second branch, while your code has integer += increment in both. So before your for-loop, define a variable direction equal to the sign of b-a (that is, if b-a >0 then direction = 1, if b-a<0 then direction = -1). Then do:

for(integer = a; (b-integer)*direction > 0; integer += direction*increment)

• Good advice. I'd write it int delta = (a < b ? +1 : -1); and then for (i = a; i != b; i += delta) { ... } – Edward Nov 16 '17 at 17:11
• @Edward this seemed to work fine until I came across the initiator being a minus number – user8786494 Nov 22 '17 at 17:50

I am not going to repeat @Accumulation's solution but instead point out another aspect. By introducing only 2 variables you can make the complicated example look like the simple one:

i = -1;
int a = i * i * i;
int b = a * i * i;
// With i * i * (i + i + i + i + i) => i * i * (5 * i) = 5 * i * i * i = 5 * a
if (a < 5 * a) {
for (integer = a; integer < 5 * a; integer += b) {
printf("%d",integer);
printf("\n");
}
} else {
for (integer = a; integer > 5 * a; integer += b) {
printf("%d",integer);
printf("\n");
}
}