# C Program to find Sum of Lower Triangle Matrix

How to write a C Program to find Sum of Lower Triangle Matrix with an example?. We already explained the lower triangle in our previous article.

## C Program to find Sum of Lower Triangle Matrix Example

This program allows the user to enter the number of rows and columns of a Matrix. Next, we are going to find the sum of the Lower triangle of this matrix using For Loop.

```/* C Program to find Sum of Lower Triangle Matrix */

#include<stdio.h>

int main()
{
int i, j, rows, columns, a, Sum = 0;

printf("\n Please Enter Number of rows and columns  :  ");
scanf("%d %d", &i, &j);

printf("\n Please Enter the Matrix Elements \n");
for(rows = 0; rows < i; rows++)
{
for(columns = 0;columns < j;columns++)
{
scanf("%d", &a[rows][columns]);
}
}

for(rows = 0; rows < i; rows++)
{
for(columns = 0; columns < j; columns++)
{
if(rows > columns)
{
Sum = Sum + a[rows][columns];
}
}
}

printf("\n The Sum of Lower Triangle Matrix = %d", Sum);
return 0;
}```

In this C Program to find Sum of Lower Triangle Matrix, We declared single Two dimensional arrays Multiplication of size of 10 * 10. I suggest you refer to the C Program to find the Lower Triangle Matrix article.

Below statements asks the User to enter the Matrix size (Number of rows and columns. For instance 2 Rows, 2 Columns = a )

```printf("\n Please Enter Number of rows and columns  :  ");
scanf("%d %d", &i, &j);```

Next, we used C Programming for loop to iterate each cell present in a matrix. Conditions inside the for loops ((rows < i) and (columns < j)) will ensure the compiler, not to exceed the matrix limit. Otherwise, the matrix will overflow

scanf statement inside the for loop will store the user entered values in every individual array element such as a, a, …..

```for(rows = 0; rows < i; rows++).
{
for(columns = 0; columns < j; columns++)
{
scanf("%d", &a[rows][columns]);
}
}```

In the next program line, We have one more for loop to find sum of Lower Triangle of a Matrix

```for(rows = 0; rows < i; rows++)
{
for(columns = 0; columns < j; columns++)
{
if(rows > columns)
{
Sum = Sum + a[rows][columns];
}
}
}```

User inserted values for C Program to find Sum of Lower Triangle Matrix are: a = {{10, 20, 30}, { 40, 50, 60},{70, 80, 90}}

Row First Iteration: for(rows = 0; rows < 3; 0++)
The condition (0 < 3) is True.

Column First Iteration: for(columns = 0; 0 < 3; 0++)
The condition (columns < 3) is True. So, it will start executing the statements inside the loop

if(rows > columns) => if(0 > 0) – This condition is False. So, it will exit from If statement

Column Second Iteration: for(columns = 1; 1 < 3; 1++)
The condition (columns < 3) is True.

if(rows > columns)=> if(0 > 1) -This condition is False.

Column Third Iteration: for(columns = 2; 2 < 3; 2++)

if(rows > columns)=> if(0 > 2) – condition is False.

Column Fourth Iteration: for(columns = 3; 3 < 3; 3++)
The condition (columns < 3) is False. So it will exit from the loop.
Next, rows value will increment to 1.

Row Second Iteration: for(rows = 1; rows < 3; 1++)
The condition (1 < 3) is True.

Column First Iteration: for(columns = 0; 0 < 3; 0++)
The condition (columns < 3) is True. So, it will start executing the statements inside the loop

if(rows > columns) => if(1 > 0) – This condition is True.
Sum  = Sum + a[rows][columns]  => 0 + 40
Sum = 40

Column Second Iteration: for(columns = 1; 1 < 3; 1++)
The condition (columns < 3) is True.

if(rows > columns)=> if(1 > 1) – condition is False.

Column Third Iteration: for(columns = 2; 2 < 3; 2++)
if(rows > columns)=> if(1 > 2) – condition is False.

Column Fourth Iteration: for(columns = 3; 3 < 3; 3++)
The condition (columns < 3) is False. So it will exit from the loop.
Next, rows value will increment to 2.

Row Third Iteration: for(rows = 2; rows < 3; 2++)
The condition (2 < 3) is True.

Column First Iteration: for(columns = 0; 0 < 3; 0++)
The condition (columns < 3) is True. So, it will start executing the statements inside the loop

if(rows > columns) => if(2 > 0) – condition is True.
Sum  = Sum + a[rows][columns]  => 40 + 70
Sum = 110

Column Second Iteration: for(columns = 1; 1 < 3; 1++)
The condition (columns < 3) is True.
if(rows > columns)=> if(2 > 1) – This condition is True.
Sum  = Sum + a[rows][columns]  => 110 + 80
Sum = 190

Column Third Iteration: for(columns = 2; 2 < 3; 2++)
if(rows > columns)=> if(2 > 2) – This condition is False.

Column Fourth Iteration: for(columns = 3; 3 < 3; 3++)
The condition (columns < 3) is False. So it will exit from the loop.

Next, rows value will increment to 3. After the increment, the condition inside the first for loop (rows < 3) will fail. So it will exit from the loop.