What general tips do you have for golfing(tips and tricks) in C?

1. Use bitwise XOR or - minus sign to check for inequality between integers:

  • if(a^b) instead of if(a!=b) save 1 character.
  • if(a-b) instead of if(a!=b) also save 1 character.

2. Abuse main's argument list to declare one or more integer variables:

main(a)
{
    for(;++a<28;)
        putchar(95+a);
}

3. The comma operator can be used to execute multiple expressions in a single block while avoiding braces:

main()
{
    int i = 0;
    int j = 1;
    if(1)
    {
        i=j,j+=1,printf("%d %d\n",i,j); // multiple statements are all executed
    }
    else
    {
        printf("failed\n");
    }
}

4. The ternary conditional operator ?: can often be used as a stand in for simple if-else statements at considerable savings:

main()
{
    int a = 10, b = 20;
    //using if else
    if (a > b)
    {
        printf("%d is bigger.",a);
    }
    else
    {
        printf("%d is bigger.",b);
    }
    //using ternary conditional operator
    printf("%d is bigger",(a>b)?a:b);
}

5. #define macros whose expansion has unbalanced braces/parentheses:

#define P printf(
main()
{
    P"Hello World");
}

6. Use *a instead of a[0] for accessing the first element of an array.

7. Combine assignment with function calls:

Instead of this:

r = 123;
printf("%d", r);

Do this:

printf("%d", r = 123);

8. Initialize multiple variables together:

Instead of this:

for(i=0,j=0;...;...)
{ 
    /* ... */ 
}

Do this:

for(i=j=0;...;...)
{
    /* ... */ 
}

9. Collapse zero/nonzero values

When you have an integer value and you need to collapse it to either 1 or 0, you can use !! to do so easily. This is sometimes advantageous for other alternatives like ?:.

Take this situation:

n=2*n+isupper(s[j])?1:0; /* 24 */

You could instead do this:

n=n*2+!!isupper(s[j]); /* 22 */

Another example:

r=R+(memcmp(b+6,"---",3)?R:0); /* 30 */

Could be rewritten as:

r=R+R*!!memcmp(b+6,"---",3)); /* 29 */

10. Avoid catastrophic function-argument type declarations

If you're declaring a function where all five arguments are ints, then life is good. you can simply write

f(a,b,c,d,e){

But suppose d needs to be a char, or even an int*. Then you're screwed! If one parameter is preceded by a type, all of them must be:

f(int a,int b,int c,int*d,int e){

But wait! There is a way around this disastrous explosion of useless characters. It goes like this:

f(a,b,c,d,e) int *d; {

This even saves on a standard main declaration if you need to use the command-line arguments:

main(c,v)char**v;{

is two bytes shorter than

main(int c,char**v){

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