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# Getting a float random number in a given range

 P: 1 I am working on a program which will need several different integer and float random numbers at different stages, for example: - At one point, I need a random number (float) in the range 0.1 to 10.0 - At one point, I need a random number (float) in the range 0.5 to 1.5 - At one point, I need a random number (float) in the range 0.3 to 3.0 - At one point, I need a random number (float) in the range 0.1 to 10.0 Also, I need to make it sure that it generates different random numbers everytime each of these functions is called in the program. For the integer random numbers, rand () is generating the same random number everytime, so I tool help from planet source code's algorithm which is as follows: ==================================== #include #include void init_mm( ); int number_range( int from, int to ); int number_mm( void ); static int rgiState[2+55]; // leave this alone int main() { init_mm(); //seed the number generator int random = number_range( 0, 1 ); cout << random << endl; } int number_mm( void ) { int *piState; int iState1; int iState2; int iRand; piState = &rgiState[2]; iState1 = piState[-2]; iState2 = piState[-1]; iRand = ( piState[iState1] + piState[iState2] ) & ( ( 1 << 30 ) - 1 ); piState[iState1] = iRand; if ( ++iState1 == 55 ) iState1 = 0; if ( ++iState2 == 55 ) iState2 = 0; piState[-2] = iState1; piState[-1] = iState2; return iRand >> 6; } /* * Generate a random number. */ int number_range( int from, int to ) { int power; int number; if ( ( to = to - from + 1 ) <= 1 ) return from; for ( power = 2; power < to; power <<= 1 ) ; while ( ( number = number_mm( ) & ( power - 1 ) ) >= to ) ; return from + number; } /* * This is the Mitchell-Moore algorithm from Knuth Volume II. */ void init_mm( ) { int *piState; int iState; piState = &rgiState[2]; piState[-2] = 55 - 55; piState[-1] = 55 - 24; piState[0] = ( (int) time( NULL ) ) & ( ( 1 << 30 ) - 1 ); piState[1] = 1; for ( iState = 2; iState < 55; iState++ ) { piState[iState] = ( piState[iState-1] + piState[iState-2] ) & ( ( 1 << 30 ) - 1 ); } return; } ========================= when i optimized the code to generate floating random numbers from 0.1 to 10.0 range, it was generating like 1.1, 2.1, 6.1 etc which is not purely random. Jun 3 '09 #1