I am wondering what does a[3] = (a[1], a[2]); does in the following code. It returns a[3] = 0. And if I eliminate the parentheses, a[3] = a[1] and a[2] doesn't change its value.
Thank you!
#include <stdio.h>
int main(int argc, char ** argv) {
int a[4] = { 100, 200 };
a[3] = (a[1], a[2]); // What happens here?
printf("%d %d %d %d\n", a[0], a[1], a[2], a[3]);
return 0;
}
What does
a[3] = (a[1], a[2]);mean?
You are assigning a[3] the result from an expression with the comma operator.
Try this example in a debugger and what is happening gets more clear
#include <stdio.h>
int main(){
int a[10] = { 100, 200 ,-10,-20,-30 };
a[3] = ( a[1]++,a[3]++,a[4]++ );
printf("%d %d %d %d\n", a[0], a[1], a[2], a[3]);
}
The first part of the expression gets executed, but in your example a[1] is ignored in this example it gets incremented, then a[3] gets assigned the last value in the parenthesis here a[4]
See more in this answer to "How does the Comma Operator work"
a[3] = (a[1], a[2]); // What happens here?
When expressions are separated by commas, the last one is returned.
int a = (1, 2, 3);
// a = 3