Can you tell me what this statement is doing?

[pairofstrings]

#define MAXVAL 50
#define COUNTER 11
main ()
{
float value[MAXVAL];
int i, low, high;
static group[COUNTER] = {0,0,0,0,0,0,0,0,0,0,0}

*/READING AND COUNTING*/

for(i=0; i<MAXVAL; i++)
{
/* READING OF VALUES*/

scanf("%f", &value);

/* COUNTING FREQUENCY OF GROUPS */

++group[ (int) (value+0.5)/10]
}

/* PRINTING OF FREQUENCY TABLE */

printf("\n");
printf(" GROUP RANGE FREQUENCY\N\N");

for(i=0; i< COUNTER; i++)
{
low = i*10;
if (i==10)
high =100;
else
high=low + 9;
printf( " %2d %3dto%3d %d)\n", i+1, low,high,group);

}

}

Can you expalin me what is ++group[ (int) (value+0.5)/10] and also what is %3d and %2d doing in the statements.output:
input data

GROUP RANGE FREQUENCY

 

[Timo]

Can you expalin me what is ++group[ (int) (value+0.5)/10]

It is equivalent to

// calculate the number of the counter for this value.
index = (int) ( value[i]+0.5 ) / 10; 
 // increase the counter by one.
group[index] += 1;

(except that the integer variable index isn't defined in your piece of code, of course).

and also what is %3d and %2d doing in the statements.

That is the format in which the number should be displayed. Google for the printf command to find out more.

 

[pairofstrings]

Can you help me trace the program? I am having little trouble in understanding this piece of code

/* COUNTING FREQUENCY OF GROUPS */

++group[ (int) (value+0.5)/10

// why are we using int in the middle of this statement?

}

/* PRINTING OF FREQUENCY TABLE */

printf("\n");
printf(" GROUP RANGE FREQUENCY\N\N");

for(i=0; i< COUNTER; i++)
{
low = i*10;
if (i==10)
high =100;
else
high=low + 9;
printf( " %2d %3dto%3d %d)\n", i+1, low,high,group);

}

}

 

[jtbell]

// why are we using int in the middle of this statement?

The calculation "(value+0.5)/10" is done using floats or doubles, which generally produces a result with a fractional part. The "(int)" casts (converts) the result to int, which discards the fraction.

 

[LudusRex]

1 0to9 5
2 10to19 7
3 20to29 12
4 30to39 8
5 40to49 6
6 50to59 3
7 60to69 1
8 70to79 2
9 80to89 4
10 90to99 2
11 100to109 0

The first line of code, "for(i=0; i<MAXVAL; i++)" is a for loop that will iterate through the array "value" for a total of MAXVAL times. This means that the loop will run for as many times as the value of MAXVAL, which is 50 in this case.

The next line, "scanf("%f", &value);" is reading in a float value from the user and storing it in the array "value" at the index i. This is done for each iteration of the for loop, so a total of MAXVAL values will be read in.

The line "++group[(int)(value+0.5)/10]" is incrementing the value stored in the array "group" at the index corresponding to the range of the value read in from the user. This line is inside the for loop, so it will be executed for each value read in. The "(int)(value+0.5)/10" part is taking the value read in, adding 0.5 to it, casting it to an integer, and then dividing it by 10 to get the range of the value. This range is then used as the index for the "group" array to increment the frequency for that range.

The lines "printf("\n");" and "printf(" GROUP RANGE FREQUENCY\N\N");" are simply printing out some formatting for the output.

The lines "low = i*10;" and "if (i==10)" are setting the lower and upper bounds for each range. Since there are 11 ranges (0-9, 10-19, 20-29, etc.), the "low" variable is multiplied by 10 to get the lower bound. The "high" variable