Done I think, C (gcc)

Language: Layout:

#include <stdio.h>
#include <math.h>
#include <sys/mman.h>
#include <pthread.h>
#include <malloc.h>
#include <stdlib.h>

int a[18][16]; //first array 
int b[16][18]; //second array
int c[18][18]; // The result

//%how to pseudo this code?

struct thread_info {
int row, col; // The row and column with respect to the element of C being solved for 
};

typedef struct thread_info thinfo;

//%Completes the arthimetic for one element of a product of matrix multiplication. 
void *compute_C_ij(void *arg)
{ 
int i, j, k, sum; //local variables for computation
thinfo *info;
   
info = (thinfo *)arg;
    
i = info->row; //is passed by the pthread call. 
j = info->col; //distinguishes which cij being solved.

//%information necessary to be passed is row of a and col of b. and which C value it is. 
sum = 0;    
        for (k = 0; k < 16; k++) {
          sum = sum + (a[i][k]*b[k][j]);
        }
 
        c[i][j] = sum;
   // printf("I = %d J= %d a = %d b = %d C= %d\n", i, j, a[i][j], b[i][j], c[i][j]); //debugging
pthread_exit(NULL); 
}

int main(void)
{
//variables to loops. 	
int i,j,k;
k = 0;
//for(k=0; k<5; k++){
   pthread_t thread[324]; //Thread variables
   thinfo info[324]; //structs to be passed
//}

//%initializing matrices a and b

for(i=0; i<18; i++){
	for(j=0; j<16; j++){
		a[i][j] = i+1+j+1;
	}
}
   
 
for(i=0; i<16; i++){
	for(j=0; j<18; j++){
		b[i][j] = i+1+(2*(j+1));
	}
}
 
//Loop to solve for each element of C = a * b concurrently. 
k=0;	
   // i=4;
     //   j=4;
for (i = 0; i < 18; i++) {		   
        for (j = 0; j < 18; j++) {
                info[k].row = i; 
                info[k].col = j;
                if (pthread_create(&thread[k], NULL, &compute_C_ij, (void *)&info[k]) != 0) {                
                printf("Error creating thread %d\n", k);
              }       
        pthread_join(thread[k], NULL);
                k++;
        }
//    k++;
	}

//Full results
//printf("The Result of matrix multiplication a * b is: \n");
//for(i=0; i<18; i++){
//	for(j=0; j<18; j++){
//		printf("%d\t", c[i][j]);
//	}
//	printf("\n");
//}

//diagonal to check with manual provided values. 
printf("The Diagonal of matrix multiplication a * b is: \n");
    for(i=0; i<18; i++){
		printf("%d", c[i][i]);
	printf("\n");
        
        
}
    
    //for(i=0; i<10; i++){
        //pthread_join(thread[k], NULL);
    //}
    pthread_exit(NULL);
}

Show compiler warnings [ + ] Compiler args [ + ] Show input
Compilation time: 0.13 sec, absolute running time: 0.07 sec, cpu time: 0.02 sec, memory peak: 3 Mb, absolute service time: 0,21 sec