Tips and Tricks for Code Golfing in C

I think that every language that is widely used in code golf should have this kind of topic. C is a popular choice for golfers, so why not share a couple of tips and tricks for this language. Most of these techniques can be used in C++ code too.

WIP: looking for additional information

  • You can write your main function without a type and return statement: main(){/*your code*/}.
  • Any of the common functions (scanf, printf, etc) can be used without including libraries.
  • You can declare variables in global space without declaring a type: a,b,c;main(). Here a, b and c will be of type int.
  • If you need to read and write data by one char, you can use read() or getchar() and write() or putchar() functions. They are shorter than scanf("%c",&c) and printf("%c",c).
  • Sometimes, you can shorten your code by using recursion instead of loops. Your main() can also be recursively used.
  • You can use a comma operator (,) for executing multiple operations in one line without using brackets: for(;;)i++,d++;.
  • Use XOR instead of != to save 1 symbol: if(a^b) same as if(a!=b).
  • Use dereferencing for reading the first element of an array: *c (2 bytes), c[0] (4 bytes).
  • You can use assignment inside any function or operator: printf("%s",(c=b)?"true":"false");.
  • Also, instead of ternary for strings, you can split them with ‘\0’ and choose the needed part: "false\0true"+1 (will choose the “true” part).
  • Sometimes, you can use bool operators in equations avoiding ifs, e.g. for comparator: (a>b)-(a<b).

:fox_face: Anyone can share any thoughts about listed tricks or send any tips for C code golfing.


You can replace chars with their ASCII index, example putchar(10) instead of putchar('\n')

You can replace for (int i=0;i<n;i++) with while(n--) if you don’t need to reuse n and you don’t need to read i

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More Tips
The first argument to main will be an integer set to 1: in main(a), a == 1.
If you use libraries, write #import<library> instead of #include<library>.
(Kind of obvious:) Use for(;;) instead of while(1) for an infinite loop.

Use scanf("%s%n",s,&a) to get the length of the input string instead of using
a=strlen(string) where a is the length use the above tricks to assign a.


The best trick in C is you can run this:

main(){system(u"bash code compressed to utf16");}


Fun killer move here :confused:

There’s a reason no one shared these tricks publicly for years.

They’re hard to find, and not documented online. So basically the few people who know them had to spend time figuring it out by themselves.
It was part of the CG golf quest to find them, part of the fun.

By giving them publicly you really kill a part of the competition, it’s a bit sad.

It’s like going to a magic show and shouting the explanations of the tricks to the audience :frowning:

At this point, just about everything here is at or near the postmortem stage. No reason not to spill the tricks when the show is closing.

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