Using Adobe Acrobat Pro: I use forms to calculate average for 21 rows and ignore empty or 0 fields.

I need to create a form that calculate the average of 21 rows but ignore the empty or 0 fields and do not include in the average.

I use this code but I get so many errors. first time to use Adobe Acrobat Pro using js 

myAverageFunction(aNames)
{
// Initialize variables

var i, v, num = 0, sum = 0;

// Loop through the input fields

for (i = 1; i <= 21; i++)
{

v = +getField("AvgCohRow1_."+ i).value;

if (v!== 0) {

// increment the non-blank/zero field counter

num++;

// add the field value to the running total

sum += v;

}

}

// Calculate the average

if (num) {

event.value = sum / num;

} else {

// All fields are empty, so set to blank

event.value = "";

}
}

event.value = myAverageFunction(["AvgCohRow1_1", "AvgCohRow1_2", "AvgCohRow1_3", "AvgCohRow1_4", "AvgCohRow1_5", "AvgCohRow1_6", "AvgCohRow1_7", "AvgCohRow1_8", "AvgCohRow1_9", "AvgCohRow1_10", "AvgCohRow1_11", "AvgCohRow1_12", "AvgCohRow1_13", "AvgCohRow1_14", "AvgCohRow1_15", "AvgCohRow1_16", "AvgCohRow1_17", "AvgCohRow1_18", "AvgCohRow1_19", "AvgCohRow1_20", "AvgCohRow1_21"]);

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ERRORS: 

TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: this.getField(...) is null
9:Field:Calculate
TypeError: this.getField(...) is null
9:Field:Calculate
TypeError: this.getField(...) is null
9:Field:Calculate
SyntaxError: missing ; before statement
19:Field:Calculate
SyntaxError: missing ; before statement
19:Field:Calculate
TypeError: this.getField(...) is null
9:Field:Calculate
TypeError: this.getField(...) is null
9:Field:Calculate
TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: this.getField(...) is null
17:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
TypeError: getField(...) is null
9:Field:Calculate
SyntaxError: return not in function
29:
SyntaxError: return not in function
29:
SyntaxError: return not in function
29:
SyntaxError: return not in function
29:
SyntaxError: missing ; before statement
1:
SyntaxError: missing ; before statement
1:
SyntaxError: missing ; before statement
1:
SyntaxError: missing ; before statement
1:
SyntaxError: missing } in compound statement
8:
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
SyntaxError: syntax error
36:
SyntaxError: syntax error
36:
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
SyntaxError: missing ; before statement
47:Field:Calculate
SyntaxError: missing ; before statement
1:Field:Calculate
SyntaxError: identifier starts immediately after numeric literal
9:
SyntaxError: identifier starts immediately after numeric literal
9:
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
SyntaxError: unterminated string literal
12:
SyntaxError: unterminated string literal
12:
SyntaxError: unterminated string literal
12:
SyntaxError: unterminated string literal
12:
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
1:Field:Calculate
ReferenceError: aNames is not defined
2:Field:Calculate