c++ - Generating random number between 4 ints -

what efficient way generate random numbers between 4 ints? ex:

it pick numbers 2 ranges 4 8 , 14 17.. thought picking middle number: 11 make randomizer have 2 options

1. add between (3-5)
2. subtract between (3-5)

i waiting replies , answers pls in c++ dont use stdio.h

if ranges inclusive, have (r1b-r1a+1)+(r2b-r2a+1) numbers choose from. use rand (or better random number library) pick non-negative integer (r1b-r1a+1)+(r2b-r2a+1) (exclusive), map result onto ranges.

int pick = rand() % ((r1b-r1a+1)+(r2b-r2a+1)); pick += ( pick < (r1b-r1a+1) ) ? r1a : r2a; 

assumptions:

• r1b >= r1a.
• r2b >= r2a.

supported:

• range 1 doesn't have before range 2.
• overlapping ranges.
• negative range endpoints.