Multiplication table with one line of code

Question

One line of code seems misleading. What I had in mind was in the form of for ( ; ; ) ; .

Having tried the lambda expression, just for fun, I coded the program below. I did this to change the third for-loop expression, where usually ++i is located, into a lambda function. The conclusion is also shown. This seems like confusing code, but it seems to work anyway. I was wondering if this can be done similarly to Java.

 for (int i=1; i<10; [](int i) {for (int j=2; j<10; ++j) printf("%dx%d=%2d ",j,i,i*j);}(i++)) printf("\n"); 2x1= 2 3x1= 3 4x1= 4 5x1= 5 6x1= 6 7x1= 7 8x1= 8 9x1= 9 2x2= 4 3x2= 6 4x2= 8 5x2=10 6x2=12 7x2=14 8x2=16 9x2=18 2x3= 6 3x3= 9 4x3=12 5x3=15 6x3=18 7x3=21 8x3=24 9x3=27 2x4= 8 3x4=12 4x4=16 5x4=20 6x4=24 7x4=28 8x4=32 9x4=36 2x5=10 3x5=15 4x5=20 5x5=25 6x5=30 7x5=35 8x5=40 9x5=45 2x6=12 3x6=18 4x6=24 5x6=30 6x6=36 7x6=42 8x6=48 9x6=54 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=49 8x7=56 9x7=63 2x8=16 3x8=24 4x8=32 5x8=40 6x8=48 7x8=56 8x8=64 9x8=72 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81 

For easier readability, I have separated the for-loop elements and the lambda function.

 for (int i=1; i<10; [](int i) { for (int j=2; j<10; ++j) printf("%dx%d=%2d ",j,i,i*j); } (i++)) { printf("\n"); } 

I tried to insert a Java lambda function similar to C ++ as (int i) -> {...} , but this does not seem to be the correct syntax for Java for-loop.

I was curious when I read the article. It is in Korean, but the code is in C ++, so I think anyone can read them. First, I get some shots of Korean drama that I don’t know about. The first figure shows Java code for multiplication. It seems that one of the actors tells the other guy that this can be done with a single line of code.

The author of the article tries, if possible in C ++. It uses multiple printf , separated by commas in the for-loop statement. I made this lambda function.

So, could this be done similarly to Java?

Answer 1

OK, I answer my question.

Unlike C ++, Java seems to be strict with respect to loop control variable statements. Entering a lambda function in any form gives an error.

So, instead, I used a single for-loop with two loop control variables, for example.

 // Single for-loop for (int i=1, j=2; i<10; i=(++j==10) ? i+1 : i, j=(j==10) ? 2 : j) System.out.format("%dx%d=%2d%c",j,i,i*j,(j==9) ? '\n' : ' '); 

Since this can be done with C ++, I was curious and compared both methods in the C ++ source and their assembler.

Here is the C ++ code (indented for better readability, but ...) and

 // 1. Using lambda function for (int i=1; i<10; [](int i) {for (int j=2; j<10; ++j) printf("%dx%d=%2d ",j,i,i*j);}(i++)) printf("\n"); // 2. Using single for-loop for (int i=1, j=2; i<10; i=(++j==10) ? i+1 : i, j=(j==10) ? 2 : j) printf("%dx%d=%2d%c",j,i,i*j,(j==9) ? '\n' : ' '); 

here is the assembly (generated by NetBeans-MinGW gcc). A function with a lambda function generates less code than a single one for a loop with several ternary operators.

 ! // 1. Using lambda function ! for (int i=1; i<10; [](int i) {for (int j=2; j<10; ++j) printf("%dx%d=%2d ",j,i,i*j);}(i++)) printf("\n"); main(int, char**)() main(int, char**)+22: movl $0x1,-0xc(%ebp) main(int, char**)+29: jmp 0x40172a <main(int, char**)+65> main(int, char**)+31: movl $0x40a06f,(%esp) main(int, char**)+38: call 0x408248 <printf(char const*, ...)> main(int, char**)+43: mov -0xc(%ebp),%edx main(int, char**)+46: incl -0xc(%ebp) main(int, char**)+49: lea -0x15(%ebp),%eax main(int, char**)+52: mov %edx,(%esp) main(int, char**)+55: mov %eax,%ecx main(int, char**)+57: call 0x4016a0 <operator()(int) const> main(int, char**)+62: sub $0x4,%esp main(int, char**)+65: cmpl $0x9,-0xc(%ebp) main(int, char**)+69: setle %al main(int, char**)+72: test %al,%al main(int, char**)+74: jne 0x401708 <main(int, char**)+31> ! ! // 2. Using single for-loop ! for (int i=1, j=2; i<10; i=(++j==10) ? i+1 : i, j=(j==10) ? 2 : j) printf("%dx%d=%2d%c",j,i,i*j,(j==9) ? '\n' : ' '); main(int, char**)+76: movl $0x1,-0x10(%ebp) main(int, char**)+83: movl $0x2,-0x14(%ebp) main(int, char**)+90: jmp 0x4017a8 <main(int, char**)+191> main(int, char**)+92: cmpl $0x9,-0x14(%ebp) main(int, char**)+96: jne 0x401752 <main(int, char**)+105> main(int, char**)+98: mov $0xa,%eax main(int, char**)+103: jmp 0x401757 <main(int, char**)+110> main(int, char**)+105: mov $0x20,%eax main(int, char**)+110: mov -0x10(%ebp),%edx main(int, char**)+113: imul -0x14(%ebp),%edx main(int, char**)+117: mov %eax,0x10(%esp) main(int, char**)+121: mov %edx,0xc(%esp) main(int, char**)+125: mov -0x10(%ebp),%eax main(int, char**)+128: mov %eax,0x8(%esp) main(int, char**)+132: mov -0x14(%ebp),%eax main(int, char**)+135: mov %eax,0x4(%esp) main(int, char**)+139: movl $0x40a071,(%esp) main(int, char**)+146: call 0x408248 <printf(char const*, ...)> main(int, char**)+151: incl -0x14(%ebp) main(int, char**)+154: cmpl $0xa,-0x14(%ebp) main(int, char**)+158: jne 0x40178f <main(int, char**)+166> main(int, char**)+160: mov -0x10(%ebp),%eax main(int, char**)+163: inc %eax main(int, char**)+164: jmp 0x401792 <main(int, char**)+169> main(int, char**)+166: mov -0x10(%ebp),%eax main(int, char**)+169: mov %eax,-0x10(%ebp) main(int, char**)+172: cmpl $0xa,-0x14(%ebp) main(int, char**)+176: je 0x4017a0 <main(int, char**)+183> main(int, char**)+178: mov -0x14(%ebp),%eax main(int, char**)+181: jmp 0x4017a5 <main(int, char**)+188> main(int, char**)+183: mov $0x2,%eax main(int, char**)+188: mov %eax,-0x14(%ebp) main(int, char**)+191: cmpl $0x9,-0x10(%ebp) main(int, char**)+195: setle %al main(int, char**)+198: test %al,%al main(int, char**)+200: jne 0x401745 <main(int, char**)+92>