c# - Does IF perform better than IF-ELSE? -

which 1 of these blocks of code performs better, , 1 of them more readable? i'd guess gain negligible, particularly in second block. curious.

block #1

string height; string width; if (myflag == 1) {     height = "60%";     width = "60%"; } else {     height = "80%";     width = "80%"; } 

block #2

string height = "80%"; string width = "80%"; if (myflag == 1) {     height = "60%";     width = "60%"; } 

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updated

the results when tested above code both blocks performed same

block #1

myflag = 1:   3 milliseconds myflag = 0:   3 milliseconds 

block #2

myflag = 1:   3 milliseconds myflag = 0:   3 milliseconds 

but 1 important thing noticed here(thanks matthew steeples answer here) since block of code have tested has not used variables height , width except assignment in if-else , if blocks of code block-1 , 2 respectively, the compiler has optimized il code removing if , if-else blocks in question showing invalid results our test here.

i have updated both code blocks write values of both height , width file using them again , forcing compiler run our test blocks(i hope), can observe code actual file writing part not effect our test results

this updated results, c# , il code

results

block #1

myflag = 1:   1688 milliseconds myflag = 0:   1664 milliseconds 

block #2

myflag = 1:   1700 milliseconds myflag = 0:   1677 milliseconds 

c#.net code

block #1

    public long withifandelse(int myflag)     {         stopwatch mytimer = new stopwatch();         string somestring = "";         mytimer.start();         (int = 0; < 1000000; i++)         {             string height;             string width;             if (myflag == 1)             {                 height = "60%";                 width = "60%";             }             else             {                 height = "80%";                 width = "80%";             }             somestring = "height: " + height + environment.newline + "width: " + width;         }         mytimer.stop();         file.writealltext("testifelse.txt", somestring);         return mytimer.elapsedmilliseconds;     } 

block #2

    public long withonlyif(int myflag)     {          stopwatch mytimer = new stopwatch();         string somestring = "";         mytimer.start();         (int = 0; < 1000000; i++)         {             string height = "80%";             string width = "80%";             if (myflag == 1)             {                 height = "60%";                 width = "60%";             }             somestring = "height: " + height + environment.newline + "width: " + width;         }         mytimer.stop();         file.writealltext("testif.txt", somestring);         return mytimer.elapsedmilliseconds;     } 

il code generated ildasm.exe

block #1

.method public hidebysig instance int64  withifandelse(int32 myflag) cil managed {   // code size       144 (0x90)   .maxstack  3   .locals init ([0] class [system]system.diagnostics.stopwatch mytimer,            [1] string somestring,            [2] int32 i,            [3] string height,            [4] string width,            [5] string[] cs$0$0000)   il_0000:  newobj     instance void [system]system.diagnostics.stopwatch::.ctor()   il_0005:  stloc.0   il_0006:  ldstr      ""   il_000b:  stloc.1   il_000c:  ldloc.0   il_000d:  callvirt   instance void [system]system.diagnostics.stopwatch::start()   il_0012:  ldc.i4.0   il_0013:  stloc.2   il_0014:  br.s       il_0070   il_0016:  ldarg.1   il_0017:  ldc.i4.1   il_0018:  bne.un.s   il_0029   il_001a:  ldstr      "60%"   il_001f:  stloc.3   il_0020:  ldstr      "60%"   il_0025:  stloc.s    width   il_0027:  br.s       il_0036   il_0029:  ldstr      "80%"   il_002e:  stloc.3   il_002f:  ldstr      "80%"   il_0034:  stloc.s    width   il_0036:  ldc.i4.5   il_0037:  newarr     [mscorlib]system.string   il_003c:  stloc.s    cs$0$0000   il_003e:  ldloc.s    cs$0$0000   il_0040:  ldc.i4.0   il_0041:  ldstr      "height: "   il_0046:  stelem.ref   il_0047:  ldloc.s    cs$0$0000   il_0049:  ldc.i4.1   il_004a:  ldloc.3   il_004b:  stelem.ref   il_004c:  ldloc.s    cs$0$0000   il_004e:  ldc.i4.2   il_004f:  call       string [mscorlib]system.environment::get_newline()   il_0054:  stelem.ref   il_0055:  ldloc.s    cs$0$0000   il_0057:  ldc.i4.3   il_0058:  ldstr      "width: "   il_005d:  stelem.ref   il_005e:  ldloc.s    cs$0$0000   il_0060:  ldc.i4.4   il_0061:  ldloc.s    width   il_0063:  stelem.ref   il_0064:  ldloc.s    cs$0$0000   il_0066:  call       string [mscorlib]system.string::concat(string[])   il_006b:  stloc.1   il_006c:  ldloc.2   il_006d:  ldc.i4.1   il_006e:  add   il_006f:  stloc.2   il_0070:  ldloc.2   il_0071:  ldc.i4     0xf4240   il_0076:  blt.s      il_0016   il_0078:  ldloc.0   il_0079:  callvirt   instance void [system]system.diagnostics.stopwatch::stop()   il_007e:  ldstr      "testifelse.txt"   il_0083:  ldloc.1   il_0084:  call       void [mscorlib]system.io.file::writealltext(string,                                                                    string)   il_0089:  ldloc.0   il_008a:  callvirt   instance int64 [system]system.diagnostics.stopwatch::get_elapsedmilliseconds()   il_008f:  ret } // end of method frmresearch::withifandelse 

block #2

.method public hidebysig instance int64  withonlyif(int32 myflag) cil managed {   // code size       142 (0x8e)   .maxstack  3   .locals init ([0] class [system]system.diagnostics.stopwatch mytimer,            [1] string somestring,            [2] int32 i,            [3] string height,            [4] string width,            [5] string[] cs$0$0000)   il_0000:  newobj     instance void [system]system.diagnostics.stopwatch::.ctor()   il_0005:  stloc.0   il_0006:  ldstr      ""   il_000b:  stloc.1   il_000c:  ldloc.0   il_000d:  callvirt   instance void [system]system.diagnostics.stopwatch::start()   il_0012:  ldc.i4.0   il_0013:  stloc.2   il_0014:  br.s       il_006e   il_0016:  ldstr      "80%"   il_001b:  stloc.3   il_001c:  ldstr      "80%"   il_0021:  stloc.s    width   il_0023:  ldarg.1   il_0024:  ldc.i4.1   il_0025:  bne.un.s   il_0034   il_0027:  ldstr      "60%"   il_002c:  stloc.3   il_002d:  ldstr      "60%"   il_0032:  stloc.s    width   il_0034:  ldc.i4.5   il_0035:  newarr     [mscorlib]system.string   il_003a:  stloc.s    cs$0$0000   il_003c:  ldloc.s    cs$0$0000   il_003e:  ldc.i4.0   il_003f:  ldstr      "height: "   il_0044:  stelem.ref   il_0045:  ldloc.s    cs$0$0000   il_0047:  ldc.i4.1   il_0048:  ldloc.3   il_0049:  stelem.ref   il_004a:  ldloc.s    cs$0$0000   il_004c:  ldc.i4.2   il_004d:  call       string [mscorlib]system.environment::get_newline()   il_0052:  stelem.ref   il_0053:  ldloc.s    cs$0$0000   il_0055:  ldc.i4.3   il_0056:  ldstr      "width: "   il_005b:  stelem.ref   il_005c:  ldloc.s    cs$0$0000   il_005e:  ldc.i4.4   il_005f:  ldloc.s    width   il_0061:  stelem.ref   il_0062:  ldloc.s    cs$0$0000   il_0064:  call       string [mscorlib]system.string::concat(string[])   il_0069:  stloc.1   il_006a:  ldloc.2   il_006b:  ldc.i4.1   il_006c:  add   il_006d:  stloc.2   il_006e:  ldloc.2   il_006f:  ldc.i4     0xf4240   il_0074:  blt.s      il_0016   il_0076:  ldloc.0   il_0077:  callvirt   instance void [system]system.diagnostics.stopwatch::stop()   il_007c:  ldstr      "testif.txt"   il_0081:  ldloc.1   il_0082:  call       void [mscorlib]system.io.file::writealltext(string,                                                                    string)   il_0087:  ldloc.0   il_0088:  callvirt   instance int64 [system]system.diagnostics.stopwatch::get_elapsedmilliseconds()   il_008d:  ret } // end of method frmresearch::withonlyif 

so can if-else block(block #1) runs faster if block(block #2) pointed many in forum.

test results

10,000,000 iterations of block 1

myflag = 0:    23.8ns per iteration myflag = 1:    23.8ns per iteration 

10,000,000 iterations of block 2

myflag = 0:    23.8ns per iteration myflag = 1:    46.8ns per iteration 

block 2 96% slower block 1. makes sense, since block 2 twice work in pessimistic case.

i prefer either case, depending on situation. if myflag rarely ever 1, want stand out edge case have handle. if both equally likely, want if-else syntax. that's preference, not fact.

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decades ago, intel 80286 dual pipeline stall if conditional jump taken, rather falling through next instruction. time of pentium went away; cpu pre-fetches both branch paths. in of mind still have twinge of fear whenever write code has common outcome in else clause. every time have remind myself doesn't matter anymore.

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int32 reps = 10000000;  private void block1(int myflag) {     string width;     string height;      stopwatch sw = new stopwatch();     sw.start();     (int = 0; < reps; i++)     {         if (myflag == 1)         {             width = string.format("{0:g}%", 60);             height = string.format("{0:g}%", 60);         }         else         {             width = string.format("{0:g}%", 80);             height = string.format("{0:g}%", 80);         }     }     sw.stop();     double time = (double)sw.elapsed.ticks / stopwatch.frequency * 1000000000.0 / reps;     messagebox.show(time.tostring() + " ns"); }  private void block2(int myflag) {     string width;     string height;      stopwatch sw = new stopwatch();     sw.start();     (int = 0; < reps; i++)     {         width = string.format("{0:g}%", 80);         height = string.format("{0:g}%", 80);         if (myflag == 1)         {             width = string.format("{0:g}%", 60);             height = string.format("{0:g}%", 60);         }     }     sw.stop();      double time = (double)sw.elapsed.ticks / stopwatch.frequency * 1000000000.0 / reps;     messagebox.show(time.tostring() + " ns"); } 

• string.format makes if 96% slower
• getpercentagestring(0.60) makes if 96% slower

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const    reps = 10000000;  procedure block1(myflag: integer); var    width, height: string;    i: integer;    t1, t2: int64;    time: extended;    freq: int64; begin    queryperformancecounter(t1);    := 1 reps    begin       if myflag = 1       begin          width := '60%';          height := '60%';       end       else       begin          width := '80%';          height := '80%';       end;    end;    queryperformancecounter(t2);    queryperformancefrequency(freq);     time := (t2-t1) / freq * 1000000000 / reps;    showmessage(floattostr(time)+ 'ns'); end;  procedure block2(myflag: integer); var    width, height: string;    i: integer;    t1, t2: int64;    time: extended;    freq: int64; begin    queryperformancecounter(t1);    := 1 reps    begin       width := '80%';       height := '80%';       if myflag = 1       begin          width := '60%';          height := '60%';       end;    end;    queryperformancecounter(t2);    queryperformancefrequency(freq);     time := (t2-t1) / freq * 1000000000 / reps;    showmessage(floattostr(time)+ 'ns'); end; 

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doing twice amount of work takes twice amount of time.

answer: if not perform better if-else.

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