for (int foo =10; foo>0; foo-- ) /* down count loop is shorter */ { wibble(); } 

for (int foo =0; foo<10; foo-- ) /* up count loop is longer */ { wibble(); } 

int foo=10; if ( foo ) wibble() 

int foo=10; if ( foo==0 ) wibble() 

Now do you see why zero might be false ?

Please note this is psuedo-code and no real instruction set looks quite like this. If you know assembly you know I'm simplifying things a lot here. If you know anything about compiler design, you didn't need to read this answer. Anyone who knows anything about loop unrolling or branch prediction, the advanced class is down the hall in room 203.

for (int foo =10; foo>0; foo-- ) /* down count loop is shorter */ { wibble(); } 

for (int foo =0; foo<10; foo-- ) /* up count loop is longer */ { wibble(); } 

int foo=10; if ( foo ) wibble() 

int foo=10; if ( foo==0 ) wibble() 

Now do you see why zero might be false?

Please note this is psuedo-code and no real instruction set looks quite like this. If you know assembly you know I'm simplifying things a lot here. If you know anything about compiler design, you didn't need to read this answer. Anyone who knows anything about loop unrolling or branch prediction, the advanced class is down the hall in room 203.

0x1000 ld a 0x00 'foo=0 0x1002 call 0x1234 'call wibble() 0x1005 dec a 'foo-- 0x1006 cmp 0x0a 'compare foo to 10 ( like a subtract but we throw the result away) 0x1008 jrns -0x08 'jump back to 0x1000 if compare was negative 0x1008 

0x1000 ld a 0x10 0x1002 jz 0x3 0x1004 call 0x1234 0x1005 

Really early CPU's had small sets of flags attached to the Accumulator.

0x1000 ld a 0x00 'foo=0 0x1002 call 0x1234 'call wibble() 0x1005 dec a 'foo-- 0x1006 cmp 0x0a 'compare foo to 10 ( like a subtract but we throw the result away) 0x1008 jrns -0x08 'jump back to 0x1000 if compare was negative 0x100a 

0x1000 ld a 0x10 0x1002 jz 0x3 0x1004 call 0x1234 0x1007 

some more c source

int foo=10; if ( foo==0 ) wibble() 

and the assembly (lets assume a marginally smart compiler that can replace ==0 with no compare)

0x1000 ld a 0x10 0x1002 jz 0x3 0x1004 call 0x1234 0x1007 

Now lets try a convention of true=1

some more c source #define TRUE 1 int foo=TRUE; if ( foo==TRUE ) wibble()

and the assembly

0x1000 ld a 0x1 0x1002 cmp a 0x01 0x1004 jz 0x3 0x1006 call 0x1234 0x1009 

see how short the case with nonzero true is ?

Really early CPU's had small sets of flags attached to the Accumulator.

Lets restate this. On some older CPU's you did not have to use a compare instruction for accumulator equal to ZERO, or accumulator less than zero.